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<!-- Definition and symptoms -->
<!-- Definition and symptoms -->'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.  
'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is a syndrome where people experience a range of symptoms in response to exposure to certain everyday chemicals.  


A 2017 scientific review described MCS as "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name=":27">Rossi, S; Pitidis, A (2017). "Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives". Journal of Occupational and Environmental Medicine. 60 (2): 138–146. doi:10.1097/JOM.0000000000001215. PMC 5794238. <nowiki>PMID 29111991</nowiki>.</ref>  A 2019 review described the condition as an "acquired disorder characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals, even at low doses, much lower than those that would cause a reaction in the general population."<ref name=":12">"2. Epidemiology". ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref>
A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal | last = Rossi | first = Sabrina | authorlink = | last2 = Pitidis | first2 = Alessio | authorlink2 =  | date = Feb 2018 | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>


Chemicals that are common triggers for MCS symptoms include pesticides, petrochemicals, formaldehyde and fragranced products.<ref name=":0">"1.3 Clinical features of the disease". ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref> Natural irritants like mold and wood-fire smoke are also often triggers.<ref name=":9">"1.2 Triggering of MCS", ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref>
While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">{{Cite book | url =|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|chapter-url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS | first = |location=Università degli Studi di Milano, Italy | date = 2019-05-23|pages=|edition=|isbn=}}</ref>


== MCS in ME and ME/CFS ==
Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and [[mold]].<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="1.2-trigger">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>
MCS has been described as a comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) and [[fibromyalgia]].<ref>{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref>{{Cite news|url=https://www.verywellhealth.com/fibromyalgia-comorbid-overlapping-conditions-716184|title=Illness That Come Along with Fibromyalgia & Chronic Fatigue Syndrome|last=Dellwo|first=Adrienne|authorlink=Adrienne Dellwo|date=Feb 26, 2018|work=Verywell Health|access-date=2018-08-23|archive-url=|archive-date=|dead-url=}}</ref> The [[Canadian Consensus Criteria]] for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and lists "Multiple Chemical Sensitivities (MCS)" as a comorbidity.  The [[International Consensus Criteria]] for diagnosing myalgic encephalomyelitis (ME) lists "sensitivities to food, medications, odours or chemicals" as a symptom and lists "multiple chemical sensitivities" as a comorbidity. A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and lists "Multiple Chemical Sensitivities" as a commonly comorbid condition.<ref>“Diagnosing and Treating ME/CFS” by the U.S. ME/CFS Clinician Coalition, August 2019. https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view</ref>
==Signs and symptoms ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal| year = 1999 | title = Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /> and symptoms range from mild to severely disabling,<ref name="Ch1" /><ref name="NICNAS" /><ref name="TaskForce2017">{{Citation | last = Task Force on Environmental Health | date = 2017 | url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf | title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal | last = Steinemann | first = Anne | authorlink =  | date = Mar 2018 | title = National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name="TaskForce2017" /><ref name="Loria2017">{{Cite journal | last = Loria-Kohen | first = Viviana | last2 = Marcos-Pasero | first2 = Helena | last3 = de la Iglesia | first3 = Rocío | last4 = Aguilar-Aguilar | first4 = Elena | last5 = Espinosa-Salinas | first5 = Isabel | last6 = Herranz | first6 = Jesús | last7 = Ramírez de Molina | first7 = Ana | last8 = Reglero | first8 = Guillermo | date = 2017-08-22 | title = Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref name="Gibson2016-unmet">{{Cite journal | last = Gibson | first = Pamela Reed | last2 = Leaf | first2 = Britney | last3 = Komisarcik | first3 = Victoria | date = 2016-01-12 | title = Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5 | pages = 75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref name="García2014">{{Cite journal | last = García-Sierra | first = Rosa | last2 = Álvarez-Moleiro | first2 = María | date = 2014-07-01 | title = Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2 | pages = 95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref name="Alobid2014">{{Cite journal | last = Alobid | first = Isam | last2 = Nogué | first2 = Santiago | last3 = Izquierdo-Dominguez | first3 = Adriana | last4 = Centellas | first4 = Silvia | last5 = Bernal-Sprekelsen | first5 = Manuel | last6 = Mullol | first6 = Joaquim | date = 2014-12-01 | title = Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal | last = Gibson | first = PR | author-link = | last2 = Vogel | first2 = VM  | authorlink2 =  | date = Jan 2009 | title = Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1 | pages = 72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Koch2006">{{Cite journal | last = Koch | first = Lynn | last2 = Vierstra | first2 = Courtney | last3 = Penix | first3 = Ken | date = 2006-09-01 | title = A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>


However, it is important to note that MCS has specific diagnostic criteria which do ''not'' include medication, food or odor sensitivities.<ref name="pmid10444033" />
Symptoms of MCS include [[headache]], [[migraine]], [[cognitive dysfunction|neurocognitive deficits]], [[dizziness]], [[fatigue]], [[arrhythmia|cardiac arrhythmia]], [[tachycardia]], [[hypotension]], [[hypertension]] (high blood pressure), [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], [[myalgia|muscle]] and [[Arthralgia|joint pain]], [[skin rash]]es, [[hives]], [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name="NICNAS" /><ref name="Valderrama2015" /><ref name="TaskForce2017" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal | last1 = Genuis | first1 = SJ | date = May 2013 | title = Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5 | pages = 572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291 | last2 = Ross | first2 = PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation. | last3 = Whysner | first3 = J | last4 = Covello | first4 = VT | last5 = Kuschner | first5 = M | last6 = Rifkind | first6 = AB | last7 = Sedler | first7 = MJ | last8 = Trichopoulos | first8 = D|via=}}</ref><ref name="Ross1999-Olfaction">{{cite journal|vauthors=Ross PM, Whysner J, Covello VT, Kuschner M, Rifkind AB, Sedler MJ, Trichopoulos D, Williams GM| year = 1999 | title = Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5 | pages = 467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN| year = 1999 | title = A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2 | pages = 73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book |isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp | title = A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs | date = 2010 | last=National Industrial Chemicals Notification and Assessment Scheme | last2 = Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref>
   
== Signs and symptoms ==
In 1999, an international consensus on MCS was published in ''The Archives of Environmental Health''.<ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref> The consensus was the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers, with different points of view about MCS.<ref name=":1">"1. Multiple Chemical Sensitivity (MCS): Case Definition". ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref> What they agreed upon was that the clinical characteristics of MCS should be defined as follows: [1] a chronic condition, [2] with symptoms that recur reproducibly, [3] in response to low levels of exposure, [4] to multiple and unrelated chemicals, and [5] improve or resolve when <nowiki>[[triggers]]</nowiki> are removed, [6] MCS involves symptoms in different organs.<ref name="pmid10444033" /><ref name=":1" />


The symptoms of MCS affect multiple organs and body systems,<ref name=":0" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name=":0" /><ref name=":6" /><ref name=":7">Task Force on Environmental Health (2017). ''[http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS]''. Phase 1 report. Toronto, Ontario: Ministry of Health and Long-Term Care; 2017.</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name=":19">Steinemann A. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/ Prevalence and effects of multiple chemical sensitivities in Australia]. ''Prev Med Rep'' 2018; 10: 191-4.</ref><ref name=":7" /><ref>Loria-Kohen V, Marcos-Pasero H, de la Iglesia R, et al. Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients. ''Med Clin (Barc)'' 2017.</ref><ref>Gibson PR, Leaf B, Komisarcik V. Unmet medical care needs in persons with multiple chemical sensitivity: a grounded theory of contested illness. J Nurs Educ Pract. 2016; 6(5): 75–83.</ref><ref>Sierra RG, Alvarez Moleiro M. Evaluation of suffering in individuals with multiple chemical sensitivity. Clin Y Salud 2014; 25 : 95–103.</ref><ref>Alobid I, Nogue S, Izquierdo-Dominguez A, et al. Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell. Eur Arch Otorhinolaryngol 2014; 271 : 3203–3208.</ref><ref>{{Cite journal|vauthors=Gibson PR, Vogel V|date=11 December 2008|title=Sickness‐related dysfunction in persons with self‐reported multiple chemical sensitivity at four levels of severity|journal=Journal of Clinical Nursing|volume=18, Issue 1, January 2009|issue=1|pages=72–81|doi=10.1111/j.1365-2702.2008.02439.x|pmid=19120734|url=https://semanticscholar.org/paper/cadc38894a660110a9e626f6ffc2028e216b1a81}}</ref><ref>Quality of life and capsaicin sensitivity in patients with airway symptoms induced by chemicals and scents: a longitudinal study. Environ Health Perspect 2007.</ref><ref>Koch L, Vierstra C, Penix K. A qualitative investigation of the psychosocial impact of multiple chemical sensitivity. J Appl Rehabil Couns. 2006; 37(3): 33–40.</ref>
A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmeticsbottles.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">{{Cite book | title = The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link= | url = |access-date= | date = 2017 | publisher=The text publishing company | last = Grenville | first = Kate | authorlink = |others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne, Australia | editor-last =  | editor-first = |editor1-link=|editor-last2 = |editor-first2 = }}</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation |url = https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf | title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety | date = 2009|location=United States | page = 9}}</ref>]]
=== Chemicals that trigger symptoms ===
The following substances are common triggers for adverse symptoms people with MCS:
* [[pesticide]]s (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic [[fragrance]]s and products containing fragrance (eg. fragranced deodorant)
* laundry [[detergent]]s and fabric softeners
* [[cigarette smoke]] and woodfire smoke
* [[petrochemical|petrochemical solvents]] and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some [[medication intolerance|medications]] and anesthetics
* [[air pollution]] (eg. [[black carbon]], [[nitrogen oxide]], [[ozone]])
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name="NICNAS" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book | last = Valderrama Rodríguez | first = M | last2 = Revilla López | first2 = MC | last3 = Blas Diez | first3 = MP | last4 = Vázquez Fernández del Pozo | first4 = S | last5 = Martín Sánchez | first5 = Jl | title = Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS) | date = 2015 | trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name="Ziem2018">{{Cite journal | last = Ziem | first = Grace E. | authorlink = | date = 2018-04-24 | title = Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Pigatto2019" />


Common symptoms of MCS include headache, migraine, neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, hypotension, hypertension, gastrointestinal problems, nausea, vomiting, muscle and joint pain, skin rashes, visual disturbances, seizures, asthma and anaphylaxis.<ref name=":0" /><ref name=":6">''A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs.'' Published in 2010 by the National Industrial Chemicals Notification and Assessment Scheme, Australian Government. Canberra, Australia <nowiki>http://test.nicnas.gov.au/Media/Latest_News/MCS.asp</nowiki></ref><ref name=":42">Valderrama Rodríguez M, Revilla López MC, Blas Diez MP, Vázquez Fernández del Pozo S, Martín Sánchez JI. ''Review of the scientific evidence on Multiple Chemical Sensitivity''. Spanish Ministry of health, social services and equality. The Aragon Institute of Health Sciences, Spain; 2015. p.31</ref><ref name=":7" /><ref name=":19" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology?|journal=Clinical Therapeutics|type=Review|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291}}</ref><ref>{{cite journal|vauthors=Ross PM, Whysner J, Covello VT, Kuschner M, Rifkind AB, Sedler MJ, Trichopoulos D, Williams GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref>{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref>
==Diagnosis and diagnostic criteria ==


A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathologies”.<ref name=":27" />
===International Consensus Criteria 1999===
The 1999 international consensus on MCS is the most commonly used diagnostic criteria for MCS. The consensus is based on the Cullen criteria plus a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /><ref name="pmid10444033" /> MCS is defined as:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,  
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book | title = Psychiatry: An evidence-based text | pages = 793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date= | date = 2009-11-27|publisher=CRC Press | last = Hooper | first = Malcolm | authorlink = Malcolm Hooper|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location= | editor-last = Puri | editor-first = Bassant|editor1-link=|editor-last2 = Treasaden|editor-first2 = Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
===Lacour criteria 2005===
# symptom duration of at least 6 months
# symptoms in response to at least 2 of 11 categories of chemical exposures
# at least one [[central nervous system]] symptom is present (eg [[fatigue]], [[headache]]s or [[cognitive dysfunction|neurocognitive deficits]], and one symptom from another organ system
# symptoms causing adjustments of personal lifestyle, or of social or occupational life
# symptoms occurring when exposed and improving or resolving when exposures are removed
# symptoms are triggered by exposure levels that do not induce symptoms in other individuals who are exposed to the same levels<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref><ref name="Tran2013" /><ref name="Damiami2021" />
===Diagnostic tools===
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />
===Differential diagnosis ===
A series of tests are needed to identify other potential causes of the symptoms. Particularly important to rule out are:
*[[Porphyria]]s
*[[Mastocytosis]] including systematic mastocytosis<ref name="Damiami2021">{{Cite journal | title = Italian Expert Consensus on Clinical and Therapeutic Management of Multiple Chemical Sensitivity (MCS) | date = 2021-10-27|url=https://doi.org/10.3390/ijerph182111294|journal=International Journal of Environmental Research and Public Health|volume=18|issue=21|pages=11294 | last = Damiani | first = Giovanni | last2 = Alessandrini | first2 = Marco | last3 = Caccamo | first3 = Daniela | last4 = Cormano | first4 = Andrea | last5 = Guzzi | first5 = Gianpaolo | last6 = Mazzatenta | first6 = Andrea | last7 = Micarelli | first7 = Alessandro | last8 = Migliore | first8 = Alberto | last9 = Piroli | first9 = Alba | last10 = Bianca | first10 = Margherita | last11 = Tapparo | first11 = Ottaviano|doi=10.3390/ijerph182111294|pmc=PMC8582949|pmid=34769816|issn=1660-4601}}</ref>


== Diagnosis ==
===Misdiagnosis ===
The 1999 international consensus on MCS is still the primary set of criteria used to assess a patient for MCS. To receive an MCS diagnosis, the  patient must satisfy all the following criteria: The patient has (1) a chronic condition (2) with symptoms that recur reproducibly (3) in response to low levels of exposure (4) to multiple and unrelated chemicals, (5) which improve or resolve when triggers are removed and (6) suggest a relation to different organs.<ref name="pmid10444033" /><ref name=":1" /> The Quick Environmental Exposure and Sensitivity Inventory (QEESI), is a diagnostic tool that is often used to assess a patient for these criteria.<ref name=":0" /><ref name=":1" />
Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name="NICNAS" /><ref name="TaskForce2017" />


== Treatment and management ==
==Prevalence==
At this time, there is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">"4. Management of patients with Multiple Chemical Sensitivity; 4.1 "First, do no harm": environmental chemical avoidance," ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref> There is also no scientific consensus on supportive therapies for MCS, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":10" /><ref name=":2" /><ref name=":7" /><ref name=":43">Valderrama Rodríguez M, Revilla López MC, Blas Diez MP, Vázquez Fernández del Pozo S, Martín Sánchez JI. ''Review of the scientific evidence on Multiple Chemical Sensitivity''. Spanish Ministry of health, social services and equality. The Aragon Institute of Health Sciences, Spain; 2015. p.17</ref><ref name=":6" /><ref>Ziem GE. Multiple chemical sensitivity: treatment and followup with avoidance and control of chemical exposures. ''Toxicol Ind Health'' 1992; 8(4): 73-86.</ref>
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" />]] While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="NICNAS" /> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="TaskForce2017" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC | date = May 2004 | title = Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5 | pages = 746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Bloch2007">{{Cite journal | last = Bloch | first = Richard M. | last2 = Meggs | first2 = William J. | date = 2007-01-01 | title = Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression | url =https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref name="Berg2008">{{Cite journal | last = Berg | first = Nikolaj Drimer | last2 = Linneberg | first2 = Allan | last3 = Dirksen | first3 = Asger | last4 = Elberling | first4 = Jesper | date = 2008-07-01 | title = Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population | url =https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7 | pages = 881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref name="Andersson2008">{{Cite journal | last = Andersson | first = Linus | last2 = Johansson | first2 = Åke | last3 = Millqvist | first3 = Eva | last4 = Nordin | first4 = Steven | last5 = Bende | first5 = Mats | date = 2008-10-01 | title = Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5 | pages = 690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}<ref name="Gibson2016-MH">{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM | date = Apr 6, 2016 | title = Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf | journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Rossi2018" />


There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144">{{Cite journal|last1=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=November 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review.|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144}}</ref><ref name=":10" /><ref name="titleOn Her Last Legs - New York Times">{{cite news|url=https://www.nytimes.com/2006/02/26/magazine/26wwln_diagnosis.html?_r=1&n=Top/News/Health/Diseases,%20Conditions,%20and%20Health%20Topics/Allergies&pagewanted=print&oref=slogin|title=On Her Last Legs - New York Times|last1=Sanders|first1=Lisa|date=2006-02-26|work=The New York Times|accessdate=2008-01-25}}</ref><ref name=":35">Victoria Department of Health (2011) ''Multiple Chemical Sensitivities: A guide for Victorian hospitals'', <nowiki>https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals</nowiki></ref>  
The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305 | last = Steinemann | first = AC | title = A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health | date = 2005|volume=59|issue=6|pages=300-5}}</ref><ref name="Caress2009">{{Cite journal | last = Caress | first = SM | last2 = Steinemann | first2 = AC | date = 2009-02-01 | title = Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1 | pages = 71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>


To avoid their condition being aggravated or worsened while in hospital, patients with MCS require special adjustments around chemical use, medications and anesthetics in hospitals.<ref>Fisher MM, Rose M. Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":34">NSW Health (2019) ''Fact sheet: Multiple Chemical Sensitivity Disorder.'' [https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx]  ''"What is MCS?" "What is multiple chemical sensitivit?"'' Accessed 18 Feb 2020. </ref><ref name=":36">''Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol'' <nowiki>http://www.lassentech.com/eimcspro.html</nowiki>, 1999. </ref><ref name=":37">Australian Commission on Safety and Quality in Health Care’s 2017 report ''[http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf National Safety and Quality Health Service Standards Guide for Hospitals]'' Canberra, Australia.</ref><ref name=":38">Canberra Hospital and Health Services’ [https://www.health.act.gov.au/media/3530 Clinical Procedure: Multiple Chemical Sensitivitiesf] (2017). Canberra, Australia. 
In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade. They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Steinemann2018" />
</ref><ref name=":39">WA Country Health Service Multiple Chemical Sensitivity / Chemical Hypersensitivity Guideline (2012). Perth, Australia. </ref>  


There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name=":11">"4.5 Oxygen therapy and hyperbaric Oxygen," ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref> likely because of oxidative stress<ref>Ewing JF, Maines MD. Glutathione depletion induces heme oxygenase-1 (HSP32) mRNA and protein in rat brain. ''Neurochem'' 1993; 60(4): 1512-9.</ref><ref>Horvath I, Loukides S, Wodehouse T, Kharitonov SA, Cole PJ, Barnes PJ. Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress. ''Thorax'' 1998; 53(10): 867-70.</ref> or because neural inflammation has reduced blood flow.<ref name=":11" /><ref>Gregersen P, Klausen H, Elsnab CU. Chronic toxic encephalopathy in solvent exposed painters in Denmark 1976-1980: clinical cases and social consequences after a 5-year follow-up. American journal of industrial medicine 1987; 11(4): 399-417.</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name=":11" />
In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/ | title = Danimarca: nuovo codice per la MCS | last = | first = | authorlink =  | date = 2014-10-14 | website = Infoamica|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14|url-status=}}</ref><ref name="Elberling2014-code">{{Cite journal | title = Patienter med symptomer, der er relateret til dufte og kemiske stoffer, kan nu kodes specifikt med Sundhedsvæsenets Klassifikationssystem | date = 2014-05-26|url=https://pubmed.ncbi.nlm.nih.gov/25096843/|journal=Ugeskrift for Laeger|volume=176|issue=11|pages=V10120627 | last = Elberling | first = Jesper | authorlink = | last2 = Bonde | first2 = Jens Peter Ellekilde | authorlink2 = | last3 = Vesterhauge | first3 = Søren | authorlink3 = | last4 = Bang | first4 = Søren | authorlink4 = | last5 = Linneberg | first5 = Allan | authorlink5 = | last6 = Zachariae | first6 = Claus | authorlink6 = | last7 = Johansen | first7 = Jeanne Duus | last8 = Blands | first8 = Jette | last9 = Skovbjerg | first9 = Sine|language=da|doi=|pmc=|pmid=25096843|access-date=|trans-title=A new classification code is available in the Danish health-care classification system for patients with symptoms related to chemicals and scents|issn=1603-6824|quote=|via=}}</ref>  


The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name=":22">"4.2 Therapeutic aids for subjects with disabilities for MCS", ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref>
A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name="TaskForce2017" />{{Rp|37}}<ref name="CCHS2014">Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>


The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name=":22" />
While a 2018 study at the University of Melbourne found that 1 million Australians (6.5% of adults) reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name="Pigatto2019">{{Cite journal | last = Pigatto | first = Paolo D. | last2 = Guzzi | first2 = Gianpaolo | date = 2019-06-01 | title = Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name="Steinemann2018-Aus">{{Cite journal |url=https://www.sciencedirect.com/science/article/pii/S2211335518300457 | last = Steinemann | first = A. | title=Prevalence and effects of multiple chemical sensitivities in Australia|journal=Prev Med Rep | date = 2018 | volume=10|pages=191-4|issue=|doi=10.1016/j.pmedr.2018.03.007|pmc=PMC5984225|pmid=29868366|quote=|access-date=|via=}}</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name="Steinemann2018" /><ref name="Steinemann2018-Aus" />


These aids may be especially important when sufferers live in areas where they are exposed to agricultural or urban pollution or smoke from forest fires or bushfires.
==Possible causes==
[[File:MCS-IEI-biomarker-VOCs.png|thumb|'''MCS patients versus controls: VOCs in breath'''<br>
Basal exhaled VOCs data for MCS and controls, acquired with the ORT-VOC, are shown in a density plot.<br>
Source: Mazzatenta et al. (2021). [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 Physiological Reports, 9, e15034].<ref name="Mazzatenta2021" />]]
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name="TaskForce2017" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name="TaskForce2017" />{{Rp|53}}


== Epidemiology ==
The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name="ch1.4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>
Prevalence rates for MCS vary according to the diagnostic criteria used.<ref name=":12" /><ref>"1.1.2 Studies on the prevalence of MCS in other countries." A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs. Published in 2010 by the National Industrial Chemicals Notification and Assessment Scheme, Australian Government. Canberra. <nowiki>http://test.nicnas.gov.au/Media/Latest_News/MCS.asp</nowiki></ref> What is clear is that the condition is reported across industrialized countries and it affects women more than men.<ref name=":2" /><ref>Task Force on Environmental Health (2017). ''Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS''. Phase 1 report. Toronto, Ontario: Ministry of Health and Long-Term Care; 2017. p.37</ref><ref>{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746}}</ref><ref>Berg ND, Linnegarg A, Dirksen A, Elberling J. Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population. Int Arch Occup Environ Health. 2008;81(7):881–887.</ref><ref>[https://www.livescience.com/author/sara-g-miller Miller], Sara G. [https://www.livescience.com/58760-kardashian-health-problems.html Keeping Up with the Kardashians' Health Problems] April 21, 2017.</ref><ref>Andersson L, Johansson A, Millqvist E, Nordin S, Bende M. Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers. Int J Hyg Environ Health. 2008;211(5–6):690–697</ref><ref>Bloch RM, Meggs WJ. Comorbidity patterns of self-reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression. J Nutr Environ Med. 2007;16(2):136–148.</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=6 April 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=2016:9|pages=163–172|via=}}</ref><ref>Valderrama Rodríguez M, Revilla López MC, Blas Diez MP, Vázquez Fernández del Pozo S, Martín Sánchez JI. ''Review of the scientific evidence on Multiple Chemical Sensitivity''. Spanish Ministry of health, social services and equality. The Aragon Institute of Health Sciences, Spain; 2015. pp.2,39.</ref>


The most extensive epidemiological study into MCS in the United States was in 2005.<ref name=":12" /><ref>Steinemann AC. A national population study of the prevalence of multiple chemical sensitivity. Arch Environ Health 2005; 59(6): 300-5.</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name=":12" /><ref>Steinemann AC. A national population study of the prevalence of multiple chemical sensitivity. Arch Environ Health 2005; 59(6): 300-5.</ref><ref>Caress S, Steinemann AC. Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset. Toxicol Ind Health 2009; 25:71–78.</ref>
When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}


In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name=":12" /><ref name="Steinemann_2018">Steinemann A. National Prevalence and Effects of Multiple Chemical Sensitivities. ''J Occup Environ Med'' 2018;'''60(3)''': e152-e6.</ref> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name=":12" /><ref name="Steinemann_2018" />
These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or divide.


A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref>Task Force on Environmental Health (2017). ''Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS''. Phase 1 report. Toronto, Ontario: Ministry of Health and Long-Term Care; 2017. p.37.</ref><ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>
In 2021, a small study by Mazzatenta and colleagues found breath analysis of key [[volatile organic compound]]s (VOCs) differed between MCS patients and healthy controls, raising the possibility that breath analysis may be able to diagnose MCS in future. Breath analysis can already be used to aid diagnosis for some illnesses.<ref name="Mazzatenta2021" />


In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the Danish population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref>Denmark: A new code for MCS, <nowiki>https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/</nowiki>. Published 2014. Accessed 11 Feb 2020.</ref>  
=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.
 
The [[Toxicant-induced loss of tolerance (TILT)|Toxicant-Induced Loss of Tolerance]] (TILT) hypothesis proposed by Miller (1996) uses the name TILT for multiple chemical sensitivity, and describes a two-phase process. First, there is ''either'' a single major exposure to chemicals ''or'' many smaller exposures, which then result in chemical intolerance or ''sensitization''. In the second phase, low or very low levels of exposure to chemicals cause symptoms that did not occur before sensitization.<ref name="Horowitz2014"/> According to the TILT hypothesis, [[Food intolerance|food and medication intolerances]] frequently occur along with chemical sensitivity. Miller (2021) believes that [[Mast cell activation syndrome|Mast Cell Activation Syndrome]] may account for TILT/MCS.<ref name="Miller2021"/>
{{See also|Toxicant-induced loss of tolerance (TILT)}}
 
Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name="1.2-trigger" /><ref name="NICNAS" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name="ch1.4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book | title = [[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]] | last = Pall | first = Martin L. | authorlink = Martin Pall|publisher=Routledge & Harrington Park Press | date = 2007 | isbn=978-0789023896|location=New York}}</ref><ref name="Pall2011">{{Cite journal | last = Pall | first = Martin L. | authorlink = Martin Pall | last2 = Satterlee | first2 = JD | date = 2001 | title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder |url = https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of [[limbic kindling]], neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="NICNAS" />
 
A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name="ch1.4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name="Bell1999">{{Cite journal | last = Bell | first = Iris R. | last2 = Baldwin | first2 = Carol M. | last3 = Fernandez | first3 = Mercedes | last4 = Schwartz | first4 = Gary E.R. | date = 1999-04-01 | title = Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name="Bell-kindling">{{Cite journal | last = Bell | first = IR | author-link = | last2 = Rossi | first2 = J | authorlink2 = | last3 = Gilbert | first3 = ME  | authorlink3 = | last4 = Kobal | first4 = G  | authorlink4 = | last5 = Morrow | first5 = LA  | authorlink5 = | last6 = Newlin | first6 = DB | authorlink6 = | last7 = Sorg | first7 = BA | last8 = Wood | first8 = RW | date = 1997-03-01 | title = Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs' theory of neurogenic inflammation.<ref name="Meggs2017">{{Cite journal | last = Meggs | first = William J. | date = 2017-05-09 | title = The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2 | pages = 83–89|doi=10.1089/eco.2016.0045}}</ref>
 
It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name="ch1.4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>  
 
Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref name="Reid2001">{{cite journal | title = Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6 | pages = 604–9|doi=10.1093/aje/153.6.604|pmid=11257069 | last = Reid | first = S | last2 = Hotopf | first2 = M  | authorlink2 = Matthew Hotopf | last3 = Hull | first3 = L | last4 = Ismail | first4 = K | last5 = Unwin | first5 = C | last6 = Wessely | first6 = S  | authorlink6 = Simon Wessely | date = 2001 | pmc=|quote=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref name="Gronseth2005">{{Cite journal | title = Gulf war syndrome: a toxic exposure? A systematic review | date = 2005-05-01|url=https://doi.org/10.1016/j.ncl.2004.12.011|journal=Neurologic clinics|volume=23|issue=2 | pages = 523–540 | last = Gronseth | first = Gary S|doi=10.1016/j.ncl.2004.12.011|pmid=15757795|issn=1557-9875}}</ref><ref name="VA2014" /><ref name="Spelman2012">{{Cite journal | last = Spelman | first = Juliette F. | last2 = Hunt | first2 = Stephen C. | last3 = Seal | first3 = Karen H. | last4 = Burgo-Black | first4 = A. Lucile | date = 2012-09-01 | title = Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>
 
The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name="VA2014">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf | title=Clinical practice guideline for the management of chronic multisystem illness | last = U.S. Department of Veterans Affairs, Department of Defense | date = Oct 2014}}</ref>  


While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name=":12" /><ref>Pigatto PD, Guzzi G. Prevalence and Risk Factors for MCS in Australia. ''Preventive Medicine Reports'' 2019.</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=2 July 2018|work=The University of Melbourne Newsroom|access-date=20 November 2019}}</ref><ref>Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name=":19" />
[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal | last = Rea | first = William J. | date = 2018-06-01 | title = A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin | url =http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6 | pages = 889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref name="Lieberman2006">{{Cite journal | last = Lieberman | first = Allan | last2 = Rea | first2 = William | last3 = Curtis | first3 = Luke | date = 2006-09-01 | title = Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3 | pages = 763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref name="Vojdani2003">{{Cite journal | last = Vojdani | first = Aristo | last2 = Thrasher | first2 = Jack D. | last3 = Madison | first3 = Roberta A. | last4 = Gray | first4 = Michael R. | last5 = Heuser | first5 = Gunnar | last6 = Campbell | first6 = Andrew W. | date = 2003-07-01 | title = Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7 | pages = 421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref name="WHO-Indoor2011">{{Cite book | last = Hänninen | first = Otto O. | authorlink = | date = 2001  | editor-last = Adan | editor-first = Olaf C. G. |editor2-last=Samson| editor2-first = Robert A. | title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal | last = Knibbs | first = Luke D. | authorlink = | last2 = Woldeyohannes | first2 = Solomon | authorlink2 = | last3 = Marks | first3 = Guy B. | authorlink3 = | last4 = Cowie | first4 = Christine T. | authorlink4 =  | date = 2018 | title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref name="Quansah2012">{{Cite journal | last = Quansah | first = Reginald | last2 = Jaakkola | first2 = Maritta S. | last3 = Hugg | first3 = Timo T. | last4 = Heikkinen | first4 = Sirpa A M. | last5 = Jaakkola | first5 = Jouni J.K. | date = 2012-11-07 | title = Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref name="Mendell2011">{{Cite journal | last = Mendell | first = Mark J | author-link = | last2 = Mirer | first2 = Anna G  | authorlink2 = | last3 = Cheung | first3 = Kerry | authorlink3 = | last4 = Tong | first4 = My | authorlink4 = | last5 = Douwes | first5 = Jeroen | authorlink5 =  | date = 2011-06-01 | title = Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6 | pages = 748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}


These findings suggest that, in the above countries, MCS is not a rare disease.
=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "[[dizziness]], [[seizure]]s, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name="Bell1999" /><ref name="Bell-kindling" /><ref name="Meggs2017" /><ref name="Tran2013">{{Cite journal | last = Tran | first = Marie Thi Dao | first2 = Lars | last2 = Arendt-Nielsen | first3 = Ron | last3 = Kupers | first4 = Jesper | last4 = Elberling | title = Multiple chemical sensitivity: On the scent of central sensitization|journal=International journal of hygiene and environmental health|volume=216|issue=2|pages=202-210 | date = April 2013|pmid=22487274|url=http://www.bcwomens.ca/Specialized-Services-Site/Documents/Complex%20Chronic%20Diseases%20(CCDP)/Multiple%20Chemical%20Sensitivity%20(journal%20article).pdf | doi=10.1016/j.ijheh.2012.02.010|pmc=|quote=|access-date=|via=}}</ref>


== Causes ==
William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name="Meggs2017" />
There is a lack of agreement among MCS researchers on the cause or causes of the condition.<ref name=":7" />


In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":8">Task Force on Environmental Health (2017). ''[http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS]''. Phase 1 report. Toronto, Ontario: Ministry of Health and Long-Term Care; 2017. p. 53.</ref> "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES/MCS."<ref name=":8" />
Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name="ch1.4" /><ref name="Bell1994">{{Cite journal | title = EEG responses to low-level chemicals in normals and cacosmics | date = 1994-07-01|url=https://europepmc.org/article/med/7778120|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 633–643 | last = Schwartz | first = G E | last2 = Bell | first2 = I R | last3 = Dikman | first3 = Z V | last4 = Fernandez | first4 = M | last5 = Kline | first5  = JP | last6 = Peterson | first6  = JM | last7 = Wright | first7  = KP | pmid=7778120|issn=1477-0393}}</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref name="Bell1998">{{Cite journal | title = Differential Resting Quantitative Electroencephalographic Alpha Patterns in Women with Environmental Chemical Intolerance, Depressives, and Normals | date = 1998-03-01|url=https://www.sciencedirect.com/science/article/pii/S000632239700245X|journal=Biological Psychiatry|volume=43|issue=5|pages=376–388 | last = Bell | first = Iris R | last2 = Schwartz | first2 = Gary E | last3 = Hardin | first3 = Elizabeth E | last4 = Baldwin | first4 = Carol M | last5 = Kline | first5 = John P|language=en|doi=10.1016/S0006-3223(97)00245-X|issn=0006-3223}}</ref>


One of the most thorough academic reviews of MCS research to be undertaken was published in Italy in May 2019.<ref name=":44">''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref> It said that the current predominant hypotheses about the causes of MCS were: biochemical, neuro-physiological and related to the limbic system and genetic predisposition.<ref name=":4">"1.4 Proposed mechanisms for MCS", ''[https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)].'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref>
Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name="ch1.4" /><ref name="Callender1994">{{Cite journal | title = Evaluation of chronic neurological sequelae after acute pesticide exposure using spect brain scans | date = 1994-03-01|url=https://doi.org/10.1080/15287399409531843|journal=Journal of Toxicology and Environmental Health|volume=41|issue=3|pages=275–284 | last = Callender | first = Thomas James | last2 = Morrow | first2 = Lisa | last3 = Subramanian | first3 = Kodanallur|doi=10.1080/15287399409531843|pmid=8126750|issn=0098-4108}}</ref><ref name="Callender1993">{{Cite book | title = Neurobehavioral Methods and Effects in Occupational and Environmental Health|chapter=Three-Dimensional Brain Metabolic Imaging in Patients with Toxic Encephalopathy. Presented at the Fourth International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health, July 8–11, 1991, Tokyo, Japan. | date = 1994-01-01|url=https://www.sciencedirect.com/science/article/pii/B9780120597857500478 | pages = 451–475 | last = Callender | first = Thomas J. | authorlink = | last2 = Morrow | first2 = Lisa | authorlink2 = | last3 = Subramanian | first3 = Kodanallur  | authorlink3 = | last4 = Duhon | first4 = Dan | authorlink4 = | last5 = Ristovv | first5 = Mona | authorlink5 = |isbn=978-0-12-059785-7|language=en|publisher=Academic Press | editor-last = Araki|editor-first = Shunichi|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Heuser1994">{{Cite journal | title = NeuroSPECT findings in patients exposed to neurotoxic chemicals | date = 1994-07-01|url=https://europepmc.org/article/med/7778114|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 561–571 | last = Heuser | first = G | last2 = Mena | first2 = I | last3 = Alamos | first3 = F|pmid=7778114|issn=1477-0393}}</ref><ref name="Hillert2007">{{Cite journal | title = Odor processing in multiple chemical sensitivity | date = 2007 | url=https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266|journal=Human Brain Mapping|volume=28|issue=3|pages=172–182 | last = Hillert | first = Lena | last2 = Musabasic | first2 = Vildana | last3 = Berglund | first3 = Hans | last4 = Ciumas | first4 = Carolina | last5 = Savic | first5 = Ivanka|language=en|doi=10.1002/hbm.20266|pmc=PMC6871299|pmid=16767766|issn=1097-0193}}</ref><ref name="Ross1999-neurotoxic">{{Cite journal | title = Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities† | date = 1999-04-01|url=https://doi.org/10.1177/074823379901500316|journal=Toxicology and Industrial Health|volume=15|issue=3-4 | pages = 415–420 | last = Ross | first = Gerald H. | last2 = Rea | first2 = William J. | last3 = Johnson | first3 = Alfred R. | last4 = Hickey | first4 = David C. | last5 = Simon | first5 = Theodore R.|language=en|doi=10.1177/074823379901500316|issn=0748-2337}}</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name="ch1.4" /><ref name="Alessandrini2016">{{Cite journal | title = Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity | date = 2016-03-01|url=https://doi.org/10.1007/s10548-015-0453-3|journal=Brain Topography|volume=29|issue=2|pages=243–252 | last = Alessandrini | first = Marco | last2 = Micarelli | first2 = Alessandro | last3 = Chiaravalloti | first3 = Agostino | last4 = Bruno | first4 = Ernesto | last5 = Danieli | first5 = Roberta | last6 = Pierantozzi | first6 = Mariangela | last7 = Genovesi | first7 = Giuseppe | last8 = Öberg | first8 = Johanna | last9 = Pagani | first9 = Marco | last10 = Schillaci | first10 = Orazio|language=en|doi=10.1007/s10548-015-0453-3|issn=1573-6792}}</ref><ref name="Chiaravalloti2015">{{Cite journal | title = Cortical activity during olfactory stimulation in multiple chemical sensitivity: a 18F-FDG PET/CT study | date = 2015-04-01|url=https://doi.org/10.1007/s00259-014-2969-2|journal=European Journal of Nuclear Medicine and Molecular Imaging|volume=42|issue=5 | pages = 733–740 | last = Chiaravalloti | first = Agostino | last2 = Pagani | first2 = Marco | last3 = Micarelli | first3 = Alessandro | last4 = Di Pietro | first4 = Barbara | last5 = Genovesi | first5 = Giuseppe | last6 = Alessandrini | first6 = Marco | last7 = Schillaci | first7 = Orazio|language=en|doi=10.1007/s00259-014-2969-2|issn=1619-7089}}</ref>


Some researchers say a consensus that the causes are multifactorial has been reached.<ref name=":3">"[https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22 Biotoxin related illnesses in Australia]", comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport. 9 August 2018. Canberra. By authority of the House of Representatives, Hansard Records. p.12.</ref>
In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.<ref name="Hansard9Aug2018">{{citation | url =https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22 | title = Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport | date = Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />


When speaking at an Australian federal parliamentary inquiry into environmental illness, Dr Graeme Edwards, a representative of the Royal Australasian College of Physicians, said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors <nowiki>[...]</nowiki> unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name=":33">[https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22 "Biotoxin related illnesses in Australia"], comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport. 9 August 2018. Canberra. By authority of the House of Representatives, Hansard Records. p.11.</ref>
===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name="ch1.4" /><ref name="NICNAS" />{{Rp|22}}


=== Toxicological ===
In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref name="Albright1992">{{Cite journal | title = Is There Evidence of an Immunologic Basis for Multiple Chemical Sensitivity? | date = Sep 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800420|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=215–219 | last = Albright | first = Joseph F. | authorlink = | last2 = Goldstein | first2 = Robert A. | authorlink2 = |doi=10.1177/074823379200800420|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref><ref name="Meggs1992">{{Cite journal | title = Multiple Chemical Sensitivities and the Immune System | date = Jul 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800419|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=203–214 | last = Meggs | first = William J. | authorlink = |doi=10.1177/074823379200800419|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref name="Labarge2000">{{Cite journal | title = Multiple Chemical Sensitivity: A Review of the Theoretical and Research Literature | date = 2000-12-01|url=https://doi.org/10.1023/A:1026460726965|journal=Neuropsychology Review|volume=10|issue=4|pages=183–211 | last = Labarge | first = Andrew S. | last2 = McCaffrey | first2 = Robert J.|language=en|doi=10.1023/A:1026460726965|issn=1573-6660}}</ref>
Professor Martin L. Pall proposed that MCS had a toxicological and biochemical cause and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name=":5" />


Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in nitric oxide and the oxidative product peroxynitrite (known as the NO/ONOO cycle) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=Explaining Unexplained illnesses:Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others.|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York|pages=}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation— processes which can be driven by the NO/ONOO cycle.<ref name=":5">''A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs.'' Published in 2010 by the National Industrial Chemicals Notification and Assessment Scheme, Australian Government. Canberra, Australia. p.30-31. <nowiki>http://test.nicnas.gov.au/Media/Latest_News/MCS.asp</nowiki></ref>
More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name="ch1.4" /><ref name="Belpomme2015">{{Cite journal | title = Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder | date = 2015-12-01|url=https://www.degruyter.com/document/doi/10.1515/reveh-2015-0027/html|journal=Reviews on Environmental Health|volume=30|issue=4|pages=251–271 | last = Belpomme | first = Dominique | last2 = Campagnac | first2 = Christine | last3 = Irigaray | first3 = Philippe|language=en|doi=10.1515/reveh-2015-0027|issn=2191-0308}}</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus. These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name="ch1.4" /><ref name="Belpomme2015" />


A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">Bell IR, Baldwin CM, Fernandez M, Schwartz GE. 1999. "Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence", ''Toxicol Ind Health'' 15:295–304.</ref><ref name=":18">Bell IR, Rossi J III, Gilbert ME, Kobal G, Morrow LA, Newlin DB, et al. 1997. "Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals," ''Environ Health Perspect'' 105(suppl):539–547.</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">Meggs WJ. The Role of Neurogenic Inflammation in Chemical Sensitivity. ''Ecopsychology'' 2017. 20. Miller CS. Toxicant-induced loss of tolerance. Addiction 2001; 96(1): 115-37.</ref> It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[Fibromyalgia|Fibromyalgia (FM)]] and [[ME/CFS|Myalgic Encephalomyelitis / Chronic Fatigue Syndrome (ME/CFS)]], and it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population.<ref>{{cite journal|vauthors=Reid S, et al|year=2001|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069}}</ref><ref name=":15" />
There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref name="ch3.11">{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="Hrda2010">{{Cite journal | title = The role of environmental factors in autoimmune thyroiditis | date = 2010 | url=https://pubmed.ncbi.nlm.nih.gov/20588228/|journal=Neuro Endocrinology Letters|volume=31|issue=3|pages=283–289 | last = Hybenova | first = Monika | last2 = Hrda | first2 = Pavlina | last3 = Procházková | first3 = Jarmila | last4 = Stejskal | first4 = Vera | last5 = Sterzl | first5 = Ivan|pmid=20588228|issn=0172-780X}}</ref><ref name="Ziem1997">{{Cite journal | title = Profile of patients with chemical injury and sensitivity. | date = 1997-03-01|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 417–436 | last = Ziem | first = G. | last2 = McTamney | first2 = J.|doi=10.1289/ehp.97105s2417|pmc=PMC1469804|pmid=9167975}}</ref><ref name="Nogue2007">{{Cite journal | title = Sensibilidad química múltiple: análisis de 52 casos | date = 2007-06-01|url=https://doi.org/10.1157/13107370|journal=Medicina clinica|volume=129|issue=3 | pages = 96–9 | last = Nogué | first = Santiago | authorlink = | last2 = Fernández-Solá | first2 = Joaquim | authorlink2 = | last3 = Rovira | first3 = Elisabet | authorlink3 = | last4 = Montori | first4 = Elisabet | authorlink4 = | last5 = Fernández-Huerta | first5 = José Manuel | authorlink5 = | last6 = Munné | first6 = Pere | authorlink6 = |language=es|doi=10.1157/13107370|pmc=|pmid=17594860|access-date=|trans-title=Multiple chemical sensitivity: study of 52 cases|issn=1578-8989|quote=|via=}}</ref>


The 2019 review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref>"4.3 Reduction of risk factors". ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS).'' The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref>
=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name="TaskForce2017" /><ref name="ch1.4" /><ref name="Genuis2013" /><ref name="Tuuminen2018">{{Cite journal | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives | date = Aug 2018|url=https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=8|pages=e429 | last = Tuuminen | first = Tamara | authorlink = |language=en-US|doi=10.1097/JOM.0000000000001369|pmc=|pmid=|access-date=|issn=1076-2752|quote=|via=}}</ref><ref name="Davidoff1994" /><ref name="Bransfield2019">{{Cite journal | title = Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty | date = 2019-10-08|url=https://doi.org/10.3390/healthcare7040114|journal=Healthcare|volume=7|issue=4|pages=114 | last = Bransfield | last2 = Friedman|doi=10.3390/healthcare7040114|pmc=PMC6955780|pmid=31597359|issn=2227-9032}}</ref><ref name="Steinemann2018" /><ref name="Davidoff1996" />  


Dr. William J. Rea and other researchers<ref>Rea WI. A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin. Clin Ther 2018; 40(6). P.p 889-93.</ref><ref>Lieberman A, Rea W, Curtis L. Adverse health effects of indoor mold exposure. ''Allergy Clin Immunol'' 2006;118(3): 763; author reply 7-8.</ref><ref>Vojdani A, Thrasher JD, Madison RA, Gray MR, Heuser G, Campbell AW. Antibodies to molds and satratoxin in individuals exposed in water-damaged buildings. Arch Environ Health 2004; 58(7): 421-32.</ref><ref>"Biotoxin related illnesses in Australia". Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport. 9 August 2018. Canberra. By authority of the House of Representatives, Hansard Records.</ref> also concluded that [[mold]] and mycotoxin exposures could trigger the onset of the condition, suggesting that pesticides are not the only class of chemicals associated with triggering the onset of MCS.<ref name=":9" />
The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref name="Gots1995">{{Cite journal | last = Gots | first = Ronald E. | date = 1995-01-01 | title = Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref name="Hainge2003">{{citation | first =Kimberly | last = Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf | work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1 | date =Fall 2003 | title = Multiple chemical sensitivity|pages=3|edition=}}</ref>
# that nocebo responses may operate in MCS,<ref name="Binkley1997">{{Cite journal | last = Binkley | first = K | author-link = | last2 = Kutcher | first2 = S  | authorlink2 =  | date = Apr 1997 | title = Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4 | pages = 570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref name="Witthoft2008">[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref name="Bailer2005">{{Cite journal | title = Evidence for overlap between idiopathic environmental intolerance and somatoform disorders | date = Nov 2005|url=https://pubmed.ncbi.nlm.nih.gov/16314597|journal=Psychosomatic Medicine|volume=67|issue=6 | pages = 921–929 | last = Bailer | first = Josef | author-link = | last2 = Witthöft | first2 = Michael | authorlink2 = | last3 = Paul | first3 = Christine | authorlink3 = | last4 = Bayerl | first4 = Christiane | authorlink4 = | last5 = Rist | first5 = Fred | authorlink5 = |doi=10.1097/01.psy.0000174170.66109.b7|pmc=|pmid=16314597|access-date=|issn=1534-7796|quote=|via=}}</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name="ch1.4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name="ch1.4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name="ch1.4" /><ref name="Davidoff1994">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Fogarty | first2 = L. | authorlink2 =  | date = Sep 1994 | title = Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Keyl | first2 = P.M. | authorlink2 =  | date = May 1996 | title = Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group | url =https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>


=== Neurological ===
Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name="TaskForce2017" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref name="Gibson2011-doc">{{Cite journal | title = Physicians' perceptions and practices regarding patient reports of multiple chemical sensitivity | date = 2011 |url=https://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf | journal=ISRN nursing|volume=2011|issue= | pages = 838930 | last = Gibson | first = Pamela Reed | authorlink = | last2 = Lindberg | first2 = Amanda | authorlink2 = |doi=10.5402/2011/838930|pmc=3168894|pmid=22007328|access-date=|issn=2090-5491|quote=|via=}}</ref><ref name="Gibson2009" /><ref name="MCS-EI">{{Cite web | title = MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]|url-status=dead | url =https://www.counselingatcela.com/mcs-and-eis|archive-date = 2020-10-21|archive-url=https://web.archive.org/web/20201021235254/https://www.counselingatcela.com/mcs-and-eis|website=The Counseling Center at CELA|quote=Is MCS a mental illness? MCS is not a mental illness}}</ref><ref name="PMC2821254">{{Cite journal | last = Lavergne | first = M. Ruth | authorlink = | last2 = Cole | first2 = Donald C. | authorlink2 = | last3 = Kerr | first3 = Kathleen | authorlink3 = | last4 = Marshall | first4 = Lynn M. | authorlink4 =  | date = Feb 2010 | title = Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal | last = Caress | first = Stanley M | authorlink = | last2 = Steinemann | first2 = Anne C  | authorlink2 =  | date = 2003-09-01 | title = A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>  
Many common symptoms of MCS are neurological<ref name=":2" /><ref name="pmid30088144" /><ref name=":0" /> (for example, "dizziness, seizures, head pain, fainting, loss of coordination"<ref name=":19" />). And neurogenic inflammation and sensitization are widely thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name=":0" /><ref name=":17" /><ref name=":18" /><ref name=":16" />


William Meggs said that neurogenic inflammation was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />
The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref name="Brussels2015">''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of May 18, 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref name="nocebohh">{{citation |url = https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response | website = Harvard Health. Harvard Medical School blog | date = Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref name="Bittar2015">{{Cite journal | last = Bittar | first = Caroline | authorlink = | last2 = Nascimento | first2 = Osvaldo J.M. | authorlink2 =  | date = Jan 2015 | title = Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1 | pages = 58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>  


Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography|Electroencephalograms (EEG)]], that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.</ref>
It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,<ref name="TaskForce2017" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref name="DSM-5">{{Cite book | title = Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|language=|title-link=|url= | date = May 15, 2014|publisher=American Psychiatric Press | last = American Psychiatric Association | first = | authorlink = |oclc=|quote=|archive-url=|archive-date=|location=Washington, D.C}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref name="icd10cm-f45.8">{{Citation | url =https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 | title = Other somatoform disorders {{!}} ICD-10-CM Diagnosis Code F45.8 | date = 2020 | website = ICD-10-CM}}</ref>


Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.</ref><ref>Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.</ref><ref>Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.</ref><ref>Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.</ref><ref>Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.</ref> These abnormalities have been documented both in studies using [[Positron emission tomography|PET (Positron Emission Tomography)]] and [[Single-photon emission computed tomography|SPECT (Single Photon Emission Computed Tomography)]] scans.<ref name=":4" /><ref>Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.</ref><ref>Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40</ref>
In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name="TaskForce2017" />{{Rp|17}}


In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, an official representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.<ref name=":3" />
=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name="ch1.4" />


===Immunological===
Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name="ch1.4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name="ch1.4" /><ref name=":23">{{Cite journal | title = Role of Polymorphisms of Inducible Nitric Oxide Synthase and Endothelial Nitric Oxide Synthase in Idiopathic Environmental Intolerances | date = 2015-03-24|url=https://www.hindawi.com/journals/mi/2015/245308/|journal=Mediators of Inflammation|volume=2015 |pages=e245308 | last = De Luca | first = Chiara | last2 = Gugliandolo | first2 = Agnese | last3 = Calabrò | first3 = Carlo | last4 = Currò | first4 = Monica | last5 = Ientile | first5 = Riccardo | last6 = Raskovic | first6 = Desanka | last7 = Korkina | first7 = Ludmila | last8 = Caccamo | first8 = Daniela|language=en|doi=10.1155/2015/245308|issn=0962-9351}}</ref><ref name=":24">{{Cite journal | title = Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses | date = 2016-01-15|url=https://www.sciencedirect.com/science/article/pii/S0024320515301211|journal=Life Sciences|volume=145|pages=27–33 | last = Gugliandolo | first = Agnese | last2 = Gangemi | first2 = Chiara | last3 = Calabrò | first3 = Carlo | last4 = Vecchio | first4 = Mercurio | last5 = Di Mauro | first5 = Debora | last6 = Renis | first6 = Marcella | last7 = Ientile | first7 = Riccardo | last8 = Currò | first8 = Monica | last9 = Caccamo | first9 = Daniela|language=en|doi=10.1016/j.lfs.2015.12.028|issn=0024-3205}}</ref>
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name=":25">''A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs.'' Published in 2010 by the National Industrial Chemicals Notification and Assessment Scheme, Australian Government. Canberra, Australia. p.21 <nowiki>http://test.nicnas.gov.au/Media/Latest_News/MCS.asp</nowiki></ref> Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name=":2" /><ref name=":4" /><ref name=":25" />


In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name=":25" /><ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name=":25" /><ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref>''A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs.'' Published in 2010 by the National Industrial Chemicals Notification and Assessment Scheme, Australian Government. Canberra, Australia. p.22. <nowiki>http://test.nicnas.gov.au/Media/Latest_News/MCS.asp</nowiki></ref><ref>Graveling RA, Pilkington A, George JPK, Butler MP & Tannahill SN (1999) A review of multiple chemical sensitivity. Occup Environ Med 56:73-85.</ref><ref>Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.</ref>
Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name="ch1.4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">{{Cite journal | title = The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances | date = Jul 2011|url=https://www.mdpi.com/1660-4601/8/7/2770|journal=International Journal of Environmental Research and Public Health|volume=8|issue=7|pages=2770–2797 | last = De Luca | first = Chiara | authorlink = | last2 = Raskovic | first2 = Desanka | authorlink2 = | last3 = Pacifico | first3 = Valeria | authorlink3 = | last4 = Thai | first4 = Jeffrey Chung Sheun | authorlink4 = | last5 = Korkina | first5 = Liudmila | authorlink5 = |doi=10.3390/ijerph8072770|pmc=3155329|pmid=21845158|access-date=|issn=1660-4601|quote=|via=}}</ref><ref name="Caccamo2013">{{Cite journal | title = Xenobiotic sensor- and metabolism-related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population | date = 2013 |url=https://downloads.hindawi.com/journals/oximed/2013/831969.pdf | journal=Oxidative Medicine and Cellular Longevity|volume=2013|issue= | pages = 831969 | last = Caccamo | first = Daniela | authorlink = | last2 = Cesareo | first2 = Eleonora | authorlink2 = | last3 = Mariani | first3 = Serena | authorlink3 = | last4 = Raskovic | first4 = Desanka | authorlink4 = | last5 = Ientile | first5 = Riccardo | authorlink5 = | last6 = Currò | first6 = Monica | authorlink6 = | last7 = Korkina | first7 = Liudmila | last8 = De Luca | first8 = Chiara|doi=10.1155/2013/831969|pmc=3725911|pmid=23936614|access-date=|issn=1942-0994|quote=|via=}}</ref><ref name="Luca2014-metabolic">{{Cite journal | title = Metabolic and Genetic Screening of Electromagnetic Hypersensitive Subjects as a Feasible Tool for Diagnostics and Intervention | date = 2014-04-09|url=https://www.hindawi.com/journals/mi/2014/924184/|journal=Mediators of Inflammation|volume=2014|pages=e924184 | last = De Luca | first = Chiara | last2 = Chung Sheun Thai | first2 = Jeffrey | last3 = Raskovic | first3 = Desanka | last4 = Cesareo | first4 = Eleonora | last5 = Caccamo | first5 = Daniela | last6 = Trukhanov | first6 = Arseny | last7 = Korkina | first7 = Liudmila|language=en|doi=10.1155/2014/924184|issn=0962-9351}}</ref> including polymorphisms and differences in expression of the following: [[Cytochrome P450 2D6|CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref name="Attis2019">{{Cite web|url=https://www.karger.com/Article/FullText/497322 | title = Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity | last = D'Attis | first = S  | authorlink = | last2 = Massari | first2 = S  | authorlink2 = | date = 2019 | website = |pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14 | last3 = Mazzei | first3 = F | last4 = Maio | first4 = D | last5 = Bozzetti | first5 = MP | last6 = Vergallo | first6 = I | last7 = Mauro | first7 = S | last8 = Minelli | first8 = M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V|title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR|volume = 33|issue = 5 |pages = 971–8 |pmid = 15256524 |doi = 10.1093/ije/dyh251|journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251 | last = | first = | last2 = | first2 =  | date = 2004|pmc=|quote= | last7 = | first7 = |via=}}</ref><ref name="Schnackenberget">{{Cite journal | last = Schnakenberg | first = Eckart | last2 = Fabig | first2 = Karl-Rainer | last3 = Stanulla | first3 = Martin | last4 = Strobl | first4 = Nils | last5 = Lustig | first5 = Michael | last6 = Fabig | first6 = Nathalie | last7 = Schloot | first7 = Werner | date = 2007-02-10 | title = A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1 | pages = 6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>


More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />
These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name="ch1.4" />
===COVID-19 and Long COVID===
There have been anecdotal reports of people with [[Long COVID]], or chronic COVID, developing new allergies, including fragrance and other chemical sensitivities.<ref name="Davis2021">{{Cite journal | last = Davis | first = Hannah | authorlink = Hannah Davis | last2 = Assaf | first2 = Gina | authorlink2 = Gina Assaf | last3 = McCorkell | first3 = Lisa | authorlink3 = | last4 = Wei | first4 = Hannah  | authorlink4 = | last5 = Low | first5 = Ryan | authorlink5 = | last6 = Re’em | first6 = Yochai | authorlink6 = | last7 = Redfield | first7 = Signe | last8 = Austin | first8 = Jared | last9 = Akrami | first9 = Athena | date = 2020 | title=Characterizing Long COVID in an International Cohort: 7 Months of Symptoms and Their Impac|url=https://europepmc.org/article/PPR/PPR258069|journal=medRxiv|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>
==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/ | title = Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation | last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers | last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain | last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir | last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson | last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas | last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner | last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested | last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry | last9 =Joshi | first9 = Pradip | authorlink9 = Pradip Joshi | last10 = Powles | first10 = AC Peter | authorlink10 = A C Peter Powles | last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey | last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | pages = 7-115 | date = 2003 |  pmid = | doi = 10.1300/J092v11n01_02 | url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf}}</ref><ref name="ICC2011primer">{{citation | last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers | last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande | last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir | last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas | last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick | last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell | last7 = Staines | first7 = D | authorlink7 = Donald Staines | last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles | last9 = Speight | first9 = N | authorlink9 = Nigel Speight | last10 = Vallings | first10 = R | authorlink10 = Rosamund Vallings | last11 = Bateman | first11 =  L | authorlink11 = Lucinda Bateman | last12 = Bell | first12 = DS | authorlink12 = David Bell | last13 = Carlo-Stella | first13 =  N | authorlink13 = Nicoletta Carlo-Stella | last14 = Chia | first14 =  J | authorlink14 = John Chia | last15 = Darragh | first15 =  A | authorlink15 = Austin Darragh | last16 = Gerken | first16 =  A | authorlink16 = Anne Gerken | last17 = Jo | first17 =  D | authorlink17 = Daehyun Jo | last18 = Lewis | first18 =  DP | authorlink18 = Donald Lewis | last19 = Light | first19 = AR | authorlink19 = Alan Light | last20 = Light | first20 =  KC | authorlink20 = Kathleen Light | last21 = Marshall-Gradisnik | first21 =  S | authorlink21 = Sonya Marshall-Gradisnik | last22 = McLaren-Howard | first22 =  J | authorlink22 = John McLaren-Howard | last23 = Mena | first23 =  I | authorlink23 =  Ismael Mena | last24 = Miwa | first24 =  K | authorlink24 =  Kunihisa Miwa | last25 = Murovska | first25 =  M | authorlink25= Modra Murovska | last26 = Stevens | first26 =  SR | authorlink26 =  Staci Stevens | title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners | date = 2012| isbn = 978-0-9739335-3-6 | url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf }}</ref>  
# The [[Canadian Consensus Criteria]] (2003) for ME/CFS lists "[[New allergies and intolerances|new sensitivities to food, medications and/or chemicals]]" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for Myalgic Encephalomyelitis lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# The U.S. ME/CFS Clinician Coalition publication '''Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) (2020)''' lists "chemical sensitivity" as a symptom of ME/CFS, and MCS as a comorbidity.<ref name="USMECFS-2020">{{Cite web | last = U.S. ME/CFS Clinician Coalition | date = Jul 2020 | url = https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view | title = Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)}}.</ref>  
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name="Schwenk2004" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name="Schwenk2004" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}


There is also evidence that subjects with MCS are more likely than controls to have proper allergies<ref>Valderrama Rodríguez M, Revilla López MC, Blas Diez MP, Vázquez Fernández del Pozo S, Martín Sánchez JI. ''Review of the scientific evidence on Multiple Chemical Sensitivity''. Spanish Ministry of health, social services and equality. The Aragon Institute of Health Sciences, Spain; 2015. p.16</ref> and autoimmune diseases, and the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], psoriasis<ref>[https://www.lifeandstylemag.com/posts/kim-kardashian-psoriasis-122550/ Kim Kardashian Reveals Psoriasis Has Spread to Her Face on Twitter!] Life & Style, June 5, 2017. </ref> and atopic eczema.<ref>“3.11 Rheumatological evaluation.” The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS). The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy.</ref><ref>Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.</ref><ref>Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.</ref><ref>Nogue S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. [Multiple chemical sensitivity: study of 52 cases]. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.</ref>
In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref name="ICD10-GM">{{Cite book | title = ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&dq=%C3%9Cberempfindlichkeit%20T78.4&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4&f=false|access-date=| date = 2011 |publisher=Deutscher Ärzteverlag | last = World Health Organization | first = | authorlink = World Health Organization | last2 = DIMDI | first2 =  | authorlink2 = |veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name="Ch4.1-Noharm" /><ref name="NICNAS" /> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" /> In 2012, Denmark introduced code '''DR688A1''' for ''Symptoms related to chemicals and scents'' (Symptomer relateret til dufte og kemiske stoffer fra SKS), in the [[Medically unexplained physical symptoms|Medically Unexplained Symptoms]], under ''R68.8 Other specified general symptoms and signs''.<ref name="Elberling2014-code" />


=== Psychological ===
And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html | title = Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) | last = Centers for Disease Control | first = | authorlink = Centers for Disease Control and Prevention | date = 2019-11-19 | website = [[Centers for Disease Control and Prevention]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>
It has also been hypothesized that MCS is a psychiatric or psychosomatic disorder.
==Treatment==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name="TaskForce2017" /><ref name="Ch4.1-Noharm">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' &#91;Translated from Italian&#93;}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name="NICNAS" /><ref name="TaskForce2017" /><ref name="Valderrama2015" /><ref name="Ziem2018" /><ref name="Ch4.1-Noharm" />


The main arguments used to support these theories have been: (1) there is no certainty about biological causes of MCS, therefore it must be psychological<ref>Gots RE (1995). "Multiple chemical sensitivities--public policy". ''J. Toxicol. Clin. Toxicol''. '''33''' (2): 111–3. doi:[https://doi.org/10.3109%2F15563659509000459 10.3109/15563659509000459]. PMID [https://pubmed.ncbi.nlm.nih.gov/7897748 7897748].</ref><ref>Multiple Chemical Sensitivity By Kimberly Hainge*, ''[https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf Pesticide Update]'' Florida Department of Agriculture & Consumer Services. Vol. XXI - No. 1. Fall, 2003. "Is MCS real? Is MCS a real disease or merely a psychosomatic illness, a disorder with physical symptoms caused by a mental or emotional illness?" *Kimberly Hainge has twenty years experience in the pesticides industry. </ref> (2) that nocebo responses may operate in MCS<ref>Binkley KE, Kutcher S (1997). "Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome". ''J Allergy Clin Immunol''. '''99''' (4): 570–4. doi:[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1]. PMID [https://pubmed.ncbi.nlm.nih.gov/9111504 9111504].</ref> and (3) that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi:[https://doi.org/10.1080%2F15287390801985687 10.1080/15287390801985687]. PMID [https://pubmed.ncbi.nlm.nih.gov/18569578 18569578].</ref><ref>Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). [http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi:[https://doi.org/10.1097%2F01.psy.0000174170.66109.b7 10.1097/01.psy.0000174170.66109.b7]. PMID [https://pubmed.ncbi.nlm.nih.gov/16314597 16314597].</ref> These theories have attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref>Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369. <nowiki>https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx</nowiki></ref><ref>Davidoff AL, Fogarty L. Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature. Arch Environ Health 1994; 49(5): 316-25.</ref><ref>Bransfield RC, Friedman KJ. [[pubmed:31597359|Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty.]] ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.</ref><ref>Davidoff AL, Keyl PM. Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group. Arch Environ Health 1996; 51(3): 201-13.</ref>  
A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name="NICNAS" /><ref name="Gibson2003">{{cite journal | last = Gibson | first = PR | last2 = Elms | first2 = AN | last3 =Ruding | first3 = LA | date = 2003 | title = Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>  


The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref>Davidoff AL, Fogarty L. [[pubmed:7944561|Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature.]] ''Arch Environ Health'' 1994; 49(5): 316-25. </ref><ref>Davidoff AL, Keyl PM. [[pubmed:8687241|Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group]]. ''Arch Environ Health'' 1996.</ref>
There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name="Ch4.1-Noharm" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name="Ch4.1-Noharm" /><ref name="VictorianHosp" />


Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref>Task Force on Environmental Health (2017). Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. Toronto, Ontario: Ministry of Health and Long-Term Care; 2017, p. 48</ref><ref>Davidoff AL, Keyl PM. Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group. Arch Environ Health 1996; 51(3): 201-13.</ref><ref>Davidoff AL, Fogarty L. Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature. Arch Environ Health 1994; 49(5): 316-25.</ref><ref>Gibson PR, Lindberg A. Physicians' perceptions and practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.</ref><ref>Gibson P., Vogel VM. [https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity.]  ''Clin Nurs''. 2009 Jan;18(1):72-81. doi: 10.1111/j.1365-2702.2008.02439.x.
There is evidence that some patients with MCS have [[hypoxia|poor tissue oxygenation]] when exposed to triggers,<ref name="Ch4.5">{{Cite book |chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal | last = Horvath | first = I. | last2 = Loukides | first2 = S. | last3 = Wodehouse | first3 = T. | last4 = Kharitonov | first4 =  S.A. | last5 = Cole | first5 = P.J. | last6 = Barnes | first6 = P.J. | date = 1998-10-01 | title = Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10 | pages = 867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref name="Ewing1993">{{Cite journal | last = Ewing | first = James F. | last2 = Maines | first2 = Mahin D. | date = 1993 | title = Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain | url =https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref name="Gregersen">{{Cite journal | last = Gregersen | first = Per | last2 = Klausen | first2 = Hans | last3 = Elsnab | first3 = Charlotte Uldal | date = 1987 | title = Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up | url =https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book |trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>
</ref><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020. </ref><ref>Lavergne MR, Cole DC, Kerr K, Marshall LM. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/ Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity]. ''Can Fam Physician''. 2010 Feb;56(2):e57-65. PMID: 20154232; PMCID: PMC2821254.</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref>Caress S.M., Steinemann A.C. 2003. [[doi:10.1289/ehp.5940|A Review of a Two-Phase Population Study of Multiple Chemical Sensitivities.]] ''Environ Health Perspect'' 111:1490-1497. Excerpt: "The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior."</ref>  


The presence of nocebo responses in MCS does not indicate the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS]  (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium.  ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions<ref>[https://www.health.harvard.edu/newsletter_article/The_nocebo_response The nocebo response]. Harvard Health. Harvard Medical School blog. Published: March, 2014.  <nowiki>https://www.health.harvard.edu/newsletter_article/The_nocebo_response</nowiki> Accessed 12 Feb 2020.</ref>, like asthma, and they are known to be especially pronounced in neurological conditions.<ref>Bittar C, Nascimento O. [[pubmed:25608129|Placebo and nocebo effects in the neurological practice]]. ''Arq Neuropsiquiatr''. 2015 Jan;73(1):58-63. doi: 10.1590/0004-282X20140180. Epub 2015 Jan 1. https://www.ncbi.nlm.nih.gov/pubmed/25608129</ref>  
The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were:  
* face masks (with HEPA and VOC filters)
* portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters), and
* water purifiers.<ref name="Ch4.2" />


It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref>Task Force on Environmental Health (2017). [http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report.] Toronto, Ontario: Ministry of Health and Long-Term Care; 2017, p. 48.</ref> and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>Diagnostic and Statistical Manual of Mental Disorders 5ed (DSM-5) Hardcover – 15 May 2013 by American Psychiatric Association (Author); ISBN 978-0890425541; Edition: 5th.</ref>) nor have they been listed among somatoform disorders in the International Classification of Diseases.<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>
In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine]], a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.  


In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref>Task Force on Environmental Health (2017). [http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report.] Toronto, Ontario: Ministry of Health and Long-Term Care; 2017.p.17</ref>
== Accessibility needs==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.<ref name="Aus-HR" />


=== Genetic  ===
Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name="TaskForce2017" /><ref name="Grenvillebook" /><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/ | title = Guidelines on the Use of Perfumes and Scented Products | last = | first = | authorlink = | date = | website = University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Steinemann2018-Aus" /><ref name="Flegel2015">{{Cite journal | last = Flegel | first = Ken | last2 = Martin | first2 = James G. | date = 2015-11-03 | title = Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name="stJosephs" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref name="notsosexy">{{Cite web |at=Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern | url =https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf | title=Not so sexy. The health risks of secret ingredients in fragrance | last = The campaign for safe cosmetics|publisher=The Environmental Working Group | date = 2010}}</ref><ref name="Steinemann2019-asthma">{{Cite journal | last = Steinemann | first = Anne | last2 = Goodman | first2 = Nigel | date = 2019-06-01 | title = Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6 | pages = 643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref name="Steinemann2019-international">{{Cite journal | title = International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products | date = 2019-05-01|url=https://doi.org/10.1007/s11869-019-00672-1|journal=Air Quality, Atmosphere & Health|volume=12|issue=5 | pages = 519–527 | last = Steinemann | first = Anne|language=en|doi=10.1007/s11869-019-00672-1|issn=1873-9326}}</ref><ref name="Nazaroff2004">[https://www.sciencedirect.com/science/article/abs/pii/S1352231004002171 Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865]</ref><ref name="Kumar1995">[https://pubmed.ncbi.nlm.nih.gov/7583865 Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433]</ref><ref name="Elberling2004">[https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2133.2004.06251.x?sid=nlm%3Apubmed Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203.]</ref><ref name="Elberling2009">[https://www.sciencedirect.com/science/article/abs/pii/S1438463909000728?via%3Dihub Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.]</ref><ref name="Mendell2007">[https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2007.00478.x Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.]</ref><ref name="Schnuch2010">[https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.2009.09510.x Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.]</ref><ref name="Neuenschwander2010">[https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.200900228 Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.]</ref><ref name="Nielsen2010">[https://pubmed.ncbi.nlm.nih.gov/15910405/ Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.]</ref><ref name="Nielsen2002">[https://pubmed.ncbi.nlm.nih.gov/12122569/ Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.]</ref><ref name="Venkatachari2008">[https://pubmed.ncbi.nlm.nih.gov/18688467/ Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.]</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.


Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.</ref><ref name=":24">Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.</ref>
There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref name="mcs-cv19-quebec">{{Cite web | last = The Environmental Health Association of Quebec | date = 2020 | url=https://aseq-ehaq.ca/en/projects/mcs-covid-19/ | title = Impacts of Covid-19 Health measures on people with multiple chemical sensitivities}}</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Steinemann2018-Aus" /><ref name="Grenvillebook" /><ref name="TaskForce2017" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name="stJosephs">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />  
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />  
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref name="ch5">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS | title = [The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS] | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23 | first = | authorlink = |volume=|pages=|edition=|isbn=}}</ref><ref name="Mercy1999">{{Cite web|url=http://www.lassentech.com/eimcspro.html | title = Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol | date = Sep 1999|publisher=Mercy Medical Centers New York and California}}</ref><ref name="Fisher2008">[https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.]</ref><ref name="Rea-surgerych">{{Cite book | last = Rea | first = William J. | authorlink = William Rea | date = 1996 | chapter=41 Surgery in the chemically sensitive|volume=IV | title = Chemical Sensitivity Tools of Diagnosis and Methods of Treatment|chapter-url=https://books.google.co.uk/books?id=cbsL8cUnO_EC&lpg=PA2015&pg=PA2803#v=onepage&q&f=true|url=https://books.google.com/books/about/Chemical_Sensitivity.html?id=cbsL8cUnO_EC | editor-last = Environmental Health Center|location=Dallas, Texas|publisher=CRC Press|pages=2803-2850|isbn=0873719654}}</ref><ref name="VictorianHosp">{{citation |url = https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals | title =  Multiple Chemical Sensitivity -- A guide for Victoria hospitals | date = Aug 25, 2011|website =Victoria Department of Health}}</ref><ref name="canberra2018">{{Cite web|url = http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx | title = Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities | date = 2018 | last = ACT Department of Health|access-date= | website = | first = Canberra, Australia | authorlink=|archive-url=|archive-date=}}</ref><ref name="NSW-factsheet">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx | title = Fact sheet: Multiple Chemical Sensitivity Disorder | last = NSW Health | first = | authorlink =  | date = Sep 2, 2015 | website = NSW Health|archive-url=|archive-date=|access-date=2020-05-14}}</ref><ref name="Hosp2017">{{Cite web | last = Australian Commission on Safety and Quality in Health Care | date = 2017 | url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf | title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name="SA2016">{{Cite web|url = https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf | title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline | date = Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name="WA2019">{{Cite web |url=http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf | title=Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline | date = Sep 14, 2010|publisher=Western Australia Country Health Service.}}</ref>  


Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref>De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.</ref><ref>Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.</ref><ref>De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], NAT2, GSTM1, and PON1 and PON2.<ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | year = 2004 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine }}</ref><ref name="Schnackenberget">Schnackenberg, E. et al. (2007).[http://www.ehjournal.net/content/6/1/6 A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes.] Environmental Health.</ref>
Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name="canberra2018" /><ref name="VictorianHosp" /><ref name="WA2019" /><ref name="SA2016" /> As well, some individual hospitals have their own policies for MCS patients.<ref name="Mercy1999" /><ref name="QHC2010">[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>


These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />
=== Housing ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref name="amputated-lives">{{Cite book |chapter=The Elusive Search for a Place to Live | title = Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st|volume=|language=|title-link=|chapter-url=http://www.chemicalsensitivityfoundation.org/pdf/amputated-lives-ch2.pdf | url=|access-date= | date = November 20, 2008|publisher=Cumberland Press | last = Johnson | first =Alison | authorlink = |others=|doi=|oclc=|quote=|location=Parramatta, Australia}}</ref><ref name="Homelessness2002" /><ref name="ANRESS-2020">{{citation | title=Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy | date = Sep 2020 | first = Sharyn | last = Martin|pages=2}}</ref><ref name="Gibson2016" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name="ActionPlan2018">{{Cite web |url = https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf | title=An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)|publisher=Final Report of the Task Force on Environmental Health|location=Ottawa, Canada | date = Dec 2018}}</ref>{{Rp|12}}


== Recognition ==
A 2002 housing survey of people with MCS in the United States found that:
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes can be used to codify the condition, including: "(1) J68.9: unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and (2) T78.4: unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref>Rossi, S; Pitidis, A (2017). "Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives". Journal of Occupational and Environmental Medicine. 60 (2): 138–146. [[Digital object identifier|doi]]:10.1097/JOM.0000000000001215. [[PubMed Central|PMC]] 5794238. [[PubMed Identifier|PMID]] 29111991. p.139</ref>
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name="Homelessness2002">{{Citation | last = Environmental Health Coalition | first = | authorlink =  | date = March 11, 2002 | title = Homelessness at critical level for Western Massachusetts chemically injured|publisher=Western Massachusetts|pages=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name="ANRESS-2020" />


In 1996, an expert panel at WHO/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel "accepted the existence of a disease of unclear pathogenesis" and proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that "the condition could not be explained by a known clinical or psychic disorder."<ref name=":45" /> The panel also suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name="Gibson2016">{{Cite journal | last = Gibson | first = Pamela | authorlink =
| date = 2016-01-01 | title = A Review of the Life Impacts of Environmental Sensitivities | url = |journal=Internal Medicine Review|volume=|issue=May | page = 9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>


MCS is recognized as a discrete pathology, however, on some countries' national indexes of diseases, including in Germany, Austria and Japan.<ref>Rossi, S; Pitidis, A (2017). "Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives". ''Journal of Occupational and Environmental Medicine''. 60 (2): 138–146. [[Digital object identifier|doi]]:10.1097/JOM.0000000000001215. [[PubMed Central|PMC]] 5794238. [[PubMed Identifier|PMID]] 29111991.“''...some countries such as Germany and Austria and some agencies and provisions in the United States such as the Environmental protection Agency (EPA) and the American Disability Act (ADA) have recognized this pathology.''” p.139.</ref><ref name=":32">4. Management of patients with Multiple Chemical Sensitivity. 4.1 "First of all, do no harm": environmental chemical avoidance, ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)''. The Italian Workgroup on MCS. Published 23 May 2019. University of Milan, Italy. "''Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance."''</ref><ref name=":41">“2.5 Does MCS have a disease classification?” ''A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs.'' Published in 2010 by the National Industrial Chemicals Notification and Assessment Scheme, Australian Government. Canberra. “''In Germany, MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V) first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, Austria has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10.''” p.15</ref> And in some countries, like Sweden, chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref>Steinemann A. [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/ National Prevalence and Effects of Multiple Chemical Sensitivities]. ''J Occup Environ Med''. 2018 Mar;60(3):e152-e156. doi: 10.1097/JOM.0000000000001272. PMID: 29329146; PMCID: PMC5865484.</ref>
A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".<ref name=":3" /> Some of these included:
* [[mold illness|mold]]
* carpet
* fumes from paint
* [[pesticide]] residue
* fumes from [nearby] laundry facilities
* fumes from cleaning products in common areas and
* [[cigarette smoke]].<ref name=":3" />
People with MCS suffer as a result of their lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name="ActionPlan2018" /> The inquiry concluded that in society at large, there was little recognition of how serious and severe environmental illness could be and that there was "a discouraging shortage of services and supports" for people living with conditions like MCS.<ref name="ActionPlan2018" /> It also found that people with environmental illness commonly experienced stigma, including from landlords, who were "often skeptical about the severity and impact of their conditions.<ref name="ActionPlan2018" />{{Rp|7,12,19}}


== History ==
== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">Schwenk M. Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects. ''GMS Curr Top Otorhinolaryngol Head Neck Surg''. 2004;3:Doc05. Epub 2004 Dec 28. PMID: 22073047; PMCID: PMC3199799.</ref>  
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name="NICNAS" /><ref name="Schwenk2004">{{Cite journal | last = Schwenk | first = Michael | date = 2004 | title = Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>  


Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />
Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name="NICNAS" /><ref name="Schwenk2004" />


Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name=":27" /><ref name="pmid10444033" />
Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />


In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />  
In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name="Schwenk2004" />  


In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/Italian-MCS-Consensus.pdf ''The Italian Consensus on Multiple Chemical Sensitivity (MCS) Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)'']. The Italian Workgroup on MCS. Published 23 May 2019. Milan, Italy.</ref> This document may be the most detailed scientific review of research about MCS to date, and it goes into considerable detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup put their consensus out in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.
In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.


== Occupational health and safety  ==
== Controversy ==
Various organisations and workplaces have policies that include fragrance and/or chemical sensitivities as occupational health and safety (OH&S) issues.<ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Noted website. Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref>
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the [[real illness|reality of the illness]].<ref name="Oreskes2011">{{Cite book | title = Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=| date = 2011 |publisher=Bloomsbury | last = Oreskes | first = Naomi | authorlink = | last2 = Conway | first2 = Erik M. | authorlink2 = |quote=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">{{Cite web|website=Deadline | first =
Erik | last = Pedersen | url =https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ | title = Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs" | date = Aug 17, 2019|quote=a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.}}</ref><ref name="Dusenberry">{{cite web | last = Dusenberry | first = Maya. |url=https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science | title = An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science|publisher=PS Mag | date = Sep 20, 2018|quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers-including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care... and add to the stigma and social isolation of an already profoundly marginalized group of people.'}}</ref><ref name="wp-talk">{{Cite web | title = Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref name="WP-cap">{{Cite web|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ | title = Wikipedia captured by skeptics|website=Skeptics about skeptics|access-date=Feb 12, 2020|quote=Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained.}}</ref><ref name="rampantharassment">{{Citation | url =http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/ | title = Rampant Harassment on Wikipedia | last = Skeptical About Skeptics | first = | authorlink = | date = | website = Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation | last = Bundrant | first = Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog | date = Apr 15, 2015 |access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url = https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog | date = Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="Steinemann2018" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name="TaskForce2017" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />


The most significant of these may be the Centers for Disease Control and Prevention (CDC)—the largest health agency in the United States, which in 2009 issued an indoor air quality policy, which says: 
Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref name="siege2013">{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege | date = Jun 26, 2013|quote="In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."}}</ref>  
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name=":46">''Indoor Environment Quality Policy'', Centers for Disease Control Office of Health and Safety, 2009, United States. www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf p.9  </ref> 
 
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last = Gale | first =Richard | last2 = Null | first2 = Gary | title = Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network | date = Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref name="Lees1998">{{citation | first = Paul R | last = Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog | date = Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last = Gavura | first = Scott | title = Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog | date = Jul 3, 2014}}</ref><ref name="LeesMold2002">{{citation|last =Lees-Haley|first =Paul R. | title=Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog | date = Dec 23, 2002}}</ref><ref name="Probe1999">{{citation | title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03 | date = Jan 1, 1999 | last = D.R.Z.}}</ref><ref name="Hall-Rea">{{citation | last = Hall | first = Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref name="MacBeth2018">{{citation|last =MacBeth | first = Braden|title = Afflicted and the Tragedy of Fake Illnesses | date = Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref name="BarrettQuestionable">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Questionable Organizations: An Overview | date = Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes &quot;clinical ecology&quot; and the bogus concept of multiple chemical sensitivity.}}</ref><ref name="BarrettVulberability">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Vulnerability to Quackery | date = Jan 16, 2019}}</ref><ref name="Barrett-AAEM">{{Citation | last = Barrett | first = Stephen | title = Regulatory Actions against AAEM Members|publisher=Quackwatch blog | date = Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref name="BarrettOilyphyria">{{Citation | last = Barrett | first = Stephen | title =  The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog | date = Jan 22, 2010}}</ref><ref name="BarrettProclam">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = MCS Proclamations}}</ref><ref name="BarrettGWI-MCS">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | first2 = Ronald E | last2 = Gots | title = Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref name="BarrettFad">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Be Wary of "Fad" Diagnoses | date = Oct 6, 2018}}</ref><ref name="BarrettIndex">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis? | date = Mar 28, 2019}}</ref><ref name="BarrettCloseLook">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = A Close Look at &quot;Multiple Chemical Sensitivity&quot; | date = 1998}}</ref><ref name="resolution21">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity | date = Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Multiple Chemical Sensitivity: A Spurious Diagnosis | date = Nov 23, 2016}}</ref>
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name=":46" />  
 
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>Steinemann, A., Goodman, N. Fragranced consumer products and effects on asthmatics: an international population-based study. ''Air Qual Atmos Health'' 12, 643–649 (2019). <nowiki>https://doi.org/10.1007/s11869-019-00693-w</nowiki></ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''. in press.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref>Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017. p.30</ref> With this in mind, some experts have called for fragrance-free policies in hospitals and healthcare settings, and in some countries (like Sweden and Canada) these already exist.<ref>Bennett, Holly. [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. 2 Jul 2018. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name=":47">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017. </ref><ref name=":7" /><ref>Wilson, Sarah. [null The post you send to your] [http://www.sarahwilson.com/2017/10/alarming-things-need-know-perfume/ friends] who are STILL wearing perfume/ Sarah Wilson blog. October 5, 2017. Accessed 15 Feb 2020. </ref>
Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref name="CaseWP2009">{{citation | url =https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf | title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York | date = Nov 24, 2009}}</ref><ref name="WP-cap" /><ref name=":20">{{citation|last = Gale | first =Richard | title = Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url = http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network | date = Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref name="NcCarthyism">{{Cite web|url=https://prn.fm/stephen-barrett-medical-mccarthyism/ | title = Stephen Barrett and Medical McCarthyism|website=The Progressive Radio network blog|access-date= Feb 21, 2020}}</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name="ch1.4" />
 
While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref name="siege2013"/> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name="TaskForce2017" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name="Schwenk2004" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name="NICNAS" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name="Ch4.1-Noharm" /><ref name="VictorianHosp" /><ref name="NSW-factsheet" /><ref name="Mercy1999" /><ref name="Hosp2017" /><ref name="canberra2018" /><ref name="WA2019" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name="Aus-HR">{{citation | date = 2007 | title=Australian Human Rights Commission Access: Guidelines and information | last = Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation | last =Michaels | first = Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf | title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization | date = 2013 |quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>
 
==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ | title = "Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films | last = | first = | date = Nov 25, 2015 | website = YouTube | archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>  


== Controversy ==
It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.  
In the tradition of the ''Merchants of Doubt''—industry-funded groups deliberately casting doubt on science about environmental damage and environmental illness—MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=|volume=|language=|title-link=|url=|access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out on Wikipedia.<ref>Talk page of Wikipedia's multiple chemical sensitivity page. https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity Accessed 12 Feb 2020. </ref><ref>Gale, Richard., Null, Gary. [http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/can-trust-wikipedia-medical-skepticism/ Can we trust Wikipedia and its medical skepticism?] Originally published on the [http://prn.fm/can-trust-wikipedia-medical-skepticism/ Progressive Radio Network, August 2, 2018]. Skeptics about Skeptics blog. Accessed 12 Feb 2020. </ref><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog.  Accessed 12 Feb 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/ Rampant Harassment on Wikipedia] from the series Wikipedia captured by skeptics. Skeptics about Skeptics blog. http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/ Accessed 12 Feb 2020. </ref><ref>Bundrant, Mike. [http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/ Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias.]  [http://wikipediawarning.com/author/8381pwpadmin/ WikiWarn] blog. <abbr>April 15, 2015. Accessed 12 Feb 2020.</abbr>
</ref><ref>[https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia The rise and fall of Wikipedia.] Orthomolecular News Service. Greenmedinfo blog. 30 Sep 2020. Accessed 12 Feb 2020. </ref>


The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism<ref>Gale, Richard., Null, Gary. [http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/can-trust-wikipedia-medical-skepticism/ Can we trust Wikipedia and its medical skepticism?] Originally published on the [http://prn.fm/can-trust-wikipedia-medical-skepticism/ Progressive Radio Network, August 2, 2018]. Skeptics about Skeptics blog. Accessed 12 Feb 2020. ''"This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM). "''</ref>—for instance, have repeatedly claimed MCS is a fake disease and that MCS sufferers are prey to pseudoscientific concepts, charlatans and purveyors of pseudoscience, fringe science and quackery.<ref name=":28">[https://www.quackwatch.org/01QuackeryRelatedTopics/mcs.html Barrett, Stephen. "Multiple Chemical Sensitivity: A Spurious Diagnosis". ''"''Quackwatch blog, 2016] https://www.quackwatch.org/01QuackeryRelatedTopics/mcs.html ''[https://www.quackwatch.org/01QuackeryRelatedTopics/mcs.html Is MCS psychosomatic?" "Is MCS psychological?"]''  This article was adapted from ''A Close Look at Multiple Chemical Sensitivity,'' a booklet that can be ordered from Quackwatch, and the book ''Chemical Sensitivity: The Truth about Environmental Illness'', by Stephen Barrett and Ronald E. Gots. ''"Critics charge that these approaches are bogus and that MCS is not a valid diagnosis."''</ref><ref>Barrett, Stephen. [https://www.quackwatch.org/04ConsumerEducation/nonrecorg.html Questionable Organizations: An Overview.] Quackwatch blog. October 20, 2019. Accessed 14 Feb 2020. ''"The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity."''</ref><ref>Barrett, Stephen. [https://www.quackwatch.org/04ConsumerEducation/Nonrecorg/aaem_reg.html Regulatory Actions against AAEM Members]. Quackwatch blog. 23 Nov 2016. Accessed 14 Feb 2020. ''"The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology...most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold..."'' </ref><ref>Barrett, Stephen. [https://www.quackwatch.org/01QuackeryRelatedTopics/quackvul.html Vulnerability to Quackery]. Quackwatch blog. 16 Jan 2019. Accessed 14 Feb 2020. ''<nowiki/>'"fad diagnoses" such as..."multiple chemical sensitivity."'''</ref><ref>Barrett, Stephen. [https://www.quackwatch.org/01QuackeryRelatedTopics/porphyria.htm The Bogus Connection between "MCS" and Porphyria]. Blog quackwatch. Revised on January 22, 2010. Accessed 14 Feb 2020. </ref><ref>Barrett, Stephen. [https://www.quackwatch.org/01QuackeryRelatedTopics/mcsproc.html MCS Proclamations] Quackwatch blog. Accessed 14 Feb 2020.
With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.  
</ref><ref>Barrett, Stephen; Ronald E. Gots. [https://www.quackwatch.org/01QuackeryRelatedTopics/gws.html "Gulf War Syndrome"] Quackwatch blog. Accessed 14 Feb 2020. "Some sufferers claim to have multiple chemical sensitivity (MCS)."
</ref><ref>Barrett, Stephen. [https://www.quackwatch.org/01QuackeryRelatedTopics/fad.html Be Wary of "Fad" Diagnoses] Quackwatch blog. 6 Oct 2018. Accessed 14 Feb 2020. </ref><ref>Barrett, Stephen. [https://www.quackwatch.org/01QuackeryRelatedTopics/fadindex.html Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?] Quackwatch blog. 28 Mar 2019. Accessed 14 Feb 2020. </ref><ref>Barrett, Stephen. ''A Close Look at "Multiple Chemical Sensitivity"''. Allentown, Pa: Quackwatch Inc. 1998.</ref><ref name=":29">Barrett, Stephen. [https://www.quackwatch.org/01QuackeryRelatedTopics/nejac.html "An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity"]. October 16, 2000</ref><ref>Paul R. Lees-Haley. [https://www.quackwatch.org/01QuackeryRelatedTopics/propa.html Propaganda techniques related to enviromental scares.] Quackwatch blog. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997. Accessed 14 Feb 2020. ''"People tend to assume that sensational terms represent reality. Multiple chemical sensitiviyt and Gulf War syndrome are prime examples."'' </ref><ref name=":30">Gavura, Scott. [https://sciencebasedmedicine.org/multiple-chemical-sensitivity-separating-facts-from-fiction/ Multiple Chemical Sensitivity: Separating facts from fiction.] 'Does multiple chemical sensitivity exist? The symptoms certainly do, but it’s less clear if they are due to “chemicals.”' Blog: Science-based medicine: Exploring issues and controversies in science and medicine. July 3, 2014. Accessed 14 Feb 2020. <article id="post-32214" class="post full-post post-32214 type-post status-publish format-standard has-post-thumbnail hentry category-science-and-medicine tag-clinical-ecology tag-environmental-illness tag-fake-diseases tag-idiopathic-environmental-intolerance tag-iei tag-mcs tag-multiple-chemical-sensitivity tag-sensitivity-related-illness tag-sri"> </ref><ref>Lees-Haley, Paul R. [https://www.quackwatch.org/01QuackeryRelatedTopics/toxicmold.html Mold Neurotoxicity: Validity, Reliability and Baloney]  Quackwatch blog. 23 Dec 2002. 14 February 2020. ''"the bogus "multiple chemical sensitivity" diagnosis."''</ref><ref>[https://www.quackwatch.org/13Hx/probe/07/index.html "Multiple chemical sensitivty suffering is real, diagnosis isn't--Quackbusters"] ''Probe Newsletter,'' Issue #07-03, January 1, 1999. </ref><ref>Hall, Harriet. [https://sciencebasedmedicine.org/environmental-medicine/ Environmental Medicine – Not Your Average Specialty] Blog: Science-based medicine: Exploring issues and controversies in science and medicine. Accessed 14 Feb 2020. ''"Rea is best known for his promotion of the concept of multipel chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community."''</ref><ref>MacBeth, Braden. [https://sciencebasedmedicine.org/afflicted-and-the-tragedy-of-fake-illnesses/ ''Afflicted'' and the Tragedy of Fake Illnesses.] November 26, 2018.</ref>


The claims made by Quackwatch/SBM, however, are at odds with: (1) the current medical consensus about MCS,<ref name=":27" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name=":42" /><ref name=":44" /><ref name=":33" /> (2) conclusions of the most recent academic reviews of MCS research, which are in respected scientific journals,<ref name=":27" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS,<ref name=":45" /> national and state health agencies and hospitals and physicians' organizations.<ref name=":27" /><ref name=":41" /><ref name=":43" /><ref name=":32" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name=":33" /><ref name=":45" /><ref>HREOC (2007) ''Australian Human Rights Commission Access: Guidelines and information''. Published in 2007 by the Australian Human Rights and Equal Opportunity Commission, Canberra. www.humanrights.gov.au/publications/access-guidelinesand-information#chem</ref><ref>Hu, Howard, Banes Cornelia (2018) [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity”], University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262</ref>
“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10 | title = Todd Haynes and Julianne Moore on Safe | last = | first = | date = |website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />  


Some legal actions (including defamation suits in the U.S.) have alleged that Quackwatch, and its founder Stephen Barrett, have been actively and knowingly promoting inaccurate information on a range of medical topics on Wikipedia.<ref>[https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York. Nov 24 2009].</ref><ref name=":31">[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics Skeptics about Skeptics]</ref><ref name=":20">Gale, Richard. [https://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/ "Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine".] Originally published on the [http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/ Progressive Radio Network, April 1, 2019].</ref> And in 2003, a California Appeals Court found Barrett “to be biased and unworthy of credibility.”<ref name=":20" />
Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation | title = The 1995 film ‘Safe’ has new meaning during our coronavirus isolation | last = Di Corpo | first = Ryan | authorlink= | date = April 11, 2020 | website = |archive-url=|archive-date=|access-date = December 31, 2020}}</ref>.


==In popular culture==
===Afflicted docuseries (2018)===
''Safe'' (1995), a cult film by director Todd Haynes is an iconic depiction of MCS.
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.  


Voted best film of the nineties by The Village Voice Film Poll<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=25 November 2015|website=Film at Lincoln Center, YouTube|archive-url=|archive-date=|access-date=30 October 2019}}</ref>, and described by critics as ”the scariest film of the year”,<ref name=":13" /> “a mesmerizing horror movie”<ref>{{Cite news|url=http://www.washingtonpost.com/wp-srv/style/longterm/movies/videos/saferkempley_c026c9.htm|title=Safe|last=Kempley|first=Rita|date=4 August 1995|work=Washington Post|access-date=30 October 2019}}</ref> and “a work of feminist counter-cinema,”<ref>Geller, Theresa L. "The Hardest, The Most Difficult Film: Todd Haynes’ Safe as Feminist Film Praxis or what the fuck is this” or “An Indelible Mark: Women and the Work of Todd Haynes”, a presentation, Grinnell College, 2013. page 6.</ref> ''Safe'' depicts MCS as a destabilizing and alienating condition.
After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />  


Protagonist Carol White, played by Julianne Moore, is a homemaker who suddenly develops a range of symptoms following the renovation of her home, in an affluent suburb of polluted Los Angeles. As Carol’s symptoms worsen, the chemicals that are triggering them seem ubiquitous. Her husband is skeptical; her community indifferent and unsupportive. She So she leaves her home, possessions and world behind, and without her husband, moves to an eerie desert community for people with environmental illness.
An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url = https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries | date = Sep 18, 2018}}</ref>
{{See also|Afflicted}}


“She is so excruciatingly alone”, Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=30 October 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />
==Notable studies and publications==
*1987, Cullen, M.R. The worker with multiple chemical sensitivities: An overview<ref name="Cullen1987">{{Cite journal | title = The worker with multiple chemical sensitivities: an overview | date = Oct 1987|url=https://pubmed.ncbi.nlm.nih.gov/3313760/|journal=Occupational Medicine (Philadelphia, Pa.)|volume=2|issue=4 | pages = 655–661 | last = Cullen | first = M.R. | authorlink = |doi=|pmc=|pmid=3313760|access-date=|issn=0885-114X|quote=|via=}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/3313760 (Abstract)]
::Defines the Cullen criteria
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2005, Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref> - [https://www.sciencedirect.com/science/article/pii/S1438463905000210 (Abstract)]
::Defines the Lacour criteria. Based on the 1987 Cullen criteria.
*2014, Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity<ref name="Horowitz2014">{{Cite journal | title = Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity | date = Apr 2014|url=https://www.liebertpub.com/doi/pdf/10.1089/act.2014.20201|journal=Alternative and Complementary Therapies|volume=20|issue=2 | pages = 96–100 | last = Horowitz | first = Sala | authorlink = |doi=10.1089/act.2014.20201|pmc=|pmid=|access-date=|issn=1076-2809|quote=|via=}}</ref> [https://www.niehs.nih.gov/news/assets/docs_a_e/download_background_material_toxicantinduced_loss_of_tolerance_by_claudia_miller_508.pdf (Full text)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2016">{{Cite journal | last = | first = | authorlink = |vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al. | date = 2016-12-09 | title = Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives<ref name="Rossi2018" /> - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal | last = Viziano | first1 = A. | last2 = Micarelli | first2 = A. | last3 = Pasquantonio | first3 = G. | last4 = Della-Morte | first4 =  D. | last5 = Alessandrini | first5 = M. | date = Nov 2018 | title = Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8 | pages = 923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2019, International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products<ref name="Steinemann2019-international" /> - [https://link.springer.com/article/10.1007/s11869-019-00672-1 (Full text)]
*2021, Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity<ref name="Mazzatenta2021">{{Cite journal | title = Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity | date = 2021 | url=https://onlinelibrary.wiley.com/doi/abs/10.14814/phy2.15034|journal=Physiological Reports|volume=9|issue=18|pages=e15034 | last = Mazzatenta | first = Andrea | last2 = Pokorski | first2 = Mieczyslaw | last3 = Giulio | first3 = Camillo Di|language=en|doi=10.14814/phy2.15034|pmc=PMC8449310|pmid=34536058|issn=2051-817X}}</ref> - [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 (Full text)]
*2021, Mast cell activation may explain many cases of chemical intolerance<ref name="Miller2021">{{Cite journal | title = Mast cell activation may explain many cases of chemical intolerance | date = 2021-11-17|url=https://doi.org/10.1186/s12302-021-00570-3|journal=Environmental Sciences Europe|volume=33|issue=1|pages=129 | last = Miller | first = Claudia S. | last2 = Palmer | first2 = Raymond F. | last3 = Dempsey | first3 = Tania T. | last4 = Ashford | first4 = Nicholas A. | last5 = Afrin | first5 = Lawrence B.|language=en|doi=10.1186/s12302-021-00570-3|issn=2190-4715}}</ref> [https://link.springer.com/article/10.1186/s12302-021-00570-3 (Full text)]
*2021, Multiple Chemical Sensitivity<ref name="Zucco2021">{{Cite journal | title = Multiple Chemical Sensitivity | date = 2021-12-29|url=https://www.mdpi.com/2076-3425/12/1/46/htm|journal=Brain Sciences|volume=12|issue=1 | pages = 46 | last = Zucco | first = Gesualdo M. | last2 = Doty | first2 = Richard L.|doi=10.3390/brainsci12010046|issn=2076-3425}}</ref> [https://www.mdpi.com/2076-3425/12/1/46/htm (Full text)]


Twenty years after the film’s release, Haynes said its themes—disease and immunity in a post-industrial landscape and how recovery is a burden often put on victims of illness—were even more relevant than they were when he made the film.<ref name=":14" />
==News articles and interviews ==
*2017, [https://web.archive.org/web/20200215070226/https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world] - New Zealand Listener
::Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia's occupational health and safety regulator Workplace OHS says on its website that it is in the employers' best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers' health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”.
*2018, [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] - SBS television, Australia (Video)
*2019, [https://www.theguardian.com/lifeandstyle/2019/sep/15/fragrance-sensitivity-why-perfumed-products-can-cause-profound-health-problems Fragrance sensitivity: why perfumed products can cause profound health problems] - The Guardian
::An intolerance to manufactured scents can lead to migraines, respiratory issues and long-term sick leave. So should they be banned in public spaces?
*2020, [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds] - Melbourne University Press
*2020, [https://i.stuff.co.nz/life-style/homed/kitchen/300272316/are-scented-cleaning-products-making-you-sick Are scented cleaning products making you sick?] - Stuff NZ
*2021, [https://www.washingtonpost.com/health/medical-mysteries/headache-chemical-smell-medical-mystery/2021/09/24/16c427ea-f2ec-11eb-a49b-d96f2dac0942_story.html The unusual headaches that upended this man's life began with a new car] - The Washington Post
*2021, [https://www.smh.com.au/national/experts-disturbed-over-toxic-discovery-in-popular-makeup-products-20210626-p584k2.html Experts ‘disturbed’ over toxic discovery in popular makeup products]<ref name="Whitehead2021">{{Cite journal | title = Fluorinated Compounds in North American Cosmetics | date = 2021-07-13|url=https://doi.org/10.1021/acs.estlett.1c00240|journal=Environmental Science & Technology Letters|volume=8|issue=7 | pages = 538–544 | last = Whitehead | first = Heather D. | last2 = Venier | first2 = Marta | last3 = Wu | first3 = Yan | last4 = Eastman | first4 = Emi | last5 = Urbanik | first5 = Shannon | last6 = Diamond | first6 = Miriam L. | last7 = Shalin | first7 = Anna | last8 = Schwartz-Narbonne | first8 = Heather | last9 = Bruton | first9 = Thomas A. | last10 = Blum | first10 = Arlene | last11 = Wang | first11 = Zhanyun|doi=10.1021/acs.estlett.1c00240}}</ref> - Sydney Morning Herald


== See also ==
== See also ==
* [[Toxicant-induced loss of tolerance (TILT)]]
* [[Mast cell activation syndrome]]
* [[Sick building syndrome]]
* [[Sick building syndrome]]
* [[Development of new sensitivities]]  
* [[Mold illness]]
* [[Gulf War Illness]]
* [[New allergies and intolerances]]
* [[Psychologization]]  


== Learn more ==
== Learn more ==
*1995, [https://en.wikipedia.org/wiki/Safe_(1995_film) Safe (1995 film)]
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref>{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|dead-url=|access-date=}}</ref>
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf | title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome | last = Williams | first = Margaret | authorlink = Margaret Williams | date = Nov 10, 2010 | website = margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2016, [http://chronicfatigue.about.com/od/whyfmscfsarelinked/a/Multiple-Chemical-Sensitivity-In-Fibromyalgia-and-Chronic-Fatigue-Syndrome.htm Multiple Chemical Sensitivity in Fibromyalgia, ME/CFS]<ref>{{Cite news|url=http://chronicfatigue.about.com/od/whyfmscfsarelinked/a/Multiple-Chemical-Sensitivity-In-Fibromyalgia-and-Chronic-Fatigue-Syndrome.htm|title=Multiple Chemical Sensitivity in Fibromyalgia & ME/CFS|last=Dellwo|first=Adrienne|authorlink=Adrienne Dellwo|date=Jul 23, 2018|work=Verywell Health|access-date=2018-08-12|archive-url=|archive-date=|dead-url=}}</ref>
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*2016, [https://cfsremission.wordpress.com/2016/04/16/multiple-chemical-sensitivity/ Multiple Chemical Sensitivity]<ref>{{Cite news|url=https://cfsremission.wordpress.com/2016/04/16/multiple-chemical-sensitivity/|title=Multiple Chemical Sensitivity|last=lasseren|first=|date=2016-04-16|work=CFS Remission|access-date=2018-08-12|archive-url=|archive-date=|dead-url=|language=en-US}}</ref>
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals
 
== References ==
== References ==
{{reflist}}
{{reflist}}


[[Category:Disease]]
[[Category:Allergy signs and symptoms]]
[[Category:Potential comorbidities]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Neurological signs and symptoms]]
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[[Category:Diagnoses]]
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[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Latest revision as of 14:00, July 25, 2023

Multiple chemical sensitivity (MCS), also known as idiopathic environmental intolerances (IEI), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."[1]

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.[2]

Common triggers for MCS symptoms include pesticides, fragranced products, petrochemicals, formaldehyde and mold.[3][4]

Signs and symptoms[edit | edit source]

There is a consensus that the symptoms of MCS affect multiple organs and body systems,[3][5][6] and symptoms range from mild to severely disabling,[3][7][8] and decrease quality of life.[6][9][8][10][11][12][13][14][15]

Symptoms of MCS include headache, migraine, neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, hypotension, hypertension (high blood pressure), gastrointestinal problems, nausea, vomiting, muscle and joint pain, skin rashes, hives, visual disturbances, seizures, and asthma.[3][7][16][8][9][17][18][19] And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: headache, fatigue, confusion, depression, shortness of breath, arthralgia, myalgia, nausea, dizziness, memory problems, gastrointestinal symptoms, respiratory symptoms.[7]

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."[1]

What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.[20] To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.[21]

Chemicals that trigger symptoms[edit | edit source]

The following substances are common triggers for adverse symptoms people with MCS:

Diagnosis and diagnostic criteria[edit | edit source]

International Consensus Criteria 1999[edit | edit source]

The 1999 international consensus on MCS is the most commonly used diagnostic criteria for MCS. The consensus is based on the Cullen criteria plus a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.[3][5] MCS is defined as:

  1. a chronic condition,
  2. with symptoms that recur reproducibly
  3. in response to low levels of exposure
  4. to multiple and unrelated chemicals,
  5. which improve or resolve when triggers are removed, and
  6. with symptoms which occur in multiple organ systems.[5][3][25]

Lacour criteria 2005[edit | edit source]

  1. symptom duration of at least 6 months
  2. symptoms in response to at least 2 of 11 categories of chemical exposures
  3. at least one central nervous system symptom is present (eg fatigue, headaches or neurocognitive deficits, and one symptom from another organ system
  4. symptoms causing adjustments of personal lifestyle, or of social or occupational life
  5. symptoms occurring when exposed and improving or resolving when exposures are removed
  6. symptoms are triggered by exposure levels that do not induce symptoms in other individuals who are exposed to the same levels[26][27][28]

Diagnostic tools[edit | edit source]

The Quick Environmental Exposure and Sensitivity Inventory (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.[3]

Differential diagnosis[edit | edit source]

A series of tests are needed to identify other potential causes of the symptoms. Particularly important to rule out are:

Misdiagnosis[edit | edit source]

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.[14][7][8]

Prevalence[edit | edit source]

Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.[9]

While prevalence rates for MCS vary according to the diagnostic criteria used,[2][7] the condition is reported across industrialized countries and the data suggests it affects women more than men.[8]:37[29][30][31][32][16]:2,39[33][1]

The most extensive epidemiological study into MCS in the U.S. was in 2005.[2] It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.[2][34][35]

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade. They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.[9]

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.[36][37]

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.[8]:37[38]

While a 2018 study at the University of Melbourne found that 1 million Australians (6.5% of adults) reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.[2][24][39] The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.[9][39]

Possible causes[edit | edit source]

MCS patients versus controls: VOCs in breath
Basal exhaled VOCs data for MCS and controls, acquired with the ORT-VOC, are shown in a density plot.
Source: Mazzatenta et al. (2021). Physiological Reports, 9, e15034.[40]

In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.[8]:53 "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."[8]:53

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.[41]

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians[42] said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."[43]:11

These recent statements suggest that earlier depictions of MCS as being either biologically or psychologically caused likely set up a false dichotomy or divide.

In 2021, a small study by Mazzatenta and colleagues found breath analysis of key volatile organic compounds (VOCs) differed between MCS patients and healthy controls, raising the possibility that breath analysis may be able to diagnose MCS in future. Breath analysis can already be used to aid diagnosis for some illnesses.[40]

Toxicological[edit | edit source]

It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

The Toxicant-Induced Loss of Tolerance (TILT) hypothesis proposed by Miller (1996) uses the name TILT for multiple chemical sensitivity, and describes a two-phase process. First, there is either a single major exposure to chemicals or many smaller exposures, which then result in chemical intolerance or sensitization. In the second phase, low or very low levels of exposure to chemicals cause symptoms that did not occur before sensitization.[44] According to the TILT hypothesis, food and medication intolerances frequently occur along with chemical sensitivity. Miller (2021) believes that Mast Cell Activation Syndrome may account for TILT/MCS.[45]

Professor Martin L. Pall proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."[4][7]

Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.[41]

Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in nitric oxide and the oxidative product peroxynitrite (known as the NO/ONOO cycle) caused MCS symptoms and worsened the condition.[22][46] He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.[7]

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,[41] including Dr. Iris Bell's theory of neuronal sensitization[47][48] and William Meggs' theory of neurogenic inflammation.[49]

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including fibromyalgia (FM) and ME/CFS, and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.[41]The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."[50]

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to organophosphate pesticides, have been found to be more likely to have MCS than the general population[51][22] as well as the fact that chemical sensitivities are a known symptom reported in Gulf war syndrome or post-deployment syndrome.[52][53][54]

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.[53]

Mold and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.[55][56][57][43] Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.[58][42][59][60][61]

Neurological[edit | edit source]

Many common symptoms of MCS are neurological[1][6][3] (for example, "dizziness, seizures, head pain, fainting, loss of coordination"[9]). And neurogenic inflammation and a central sensitization syndrome have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.[3][47][48][49][27]

William Meggs said that neurogenic inflammation was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.[49]

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using Electroencephalography (EEG), that people with MCS often had certain abnormal brain wave patterns.[41][62] For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.[63]

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the autonomic nervous system areas.[41][64][65][66][67][68] These abnormalities have been documented both in studies using Positron emission tomography (PET) and Single-photon emission computed tomography (SPECT) scans.[41][69][70]

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”[43]:12[42]

Immunological[edit | edit source]

MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.[7]:21 Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.[1][41][7]:22

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.[7]:22[17] While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.[7]:22[71][72] As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.[7]:22[19][73]

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.[41][74] It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus. These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.[41][74]

There is also evidence that subjects with MCS are more likely than controls to have real allergies[16]:16 and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and Hashimoto's thyroiditis, Systemic Lupus Erythematosus (SLE), psoriasis and atopic eczema.[75][76][77][78]

Psychological[edit | edit source]

It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,[2] and the hypothesis that MCS has a psychological cause has attracted considerable criticism.[8][41][17][79][80][81][9][82]

The main arguments used to support the is that MCS has psychological causes have been:

  1. there is no certainty about biological causes of MCS, therefore it must be psychological[83][84]
  2. that nocebo responses may operate in MCS,[85] and
  3. that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.[86][87]

The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."[41] It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.[41] It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."[41][80][82]

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.[8]:48[82][80][88][14][89][90] One study showed that anxiety and depression typically started in people with MCS post onset of the condition.[91]

The presence of nocebo responses in MCS does not indicate that it is the cause of the disease.[92] Nocebo responses are found in many biologically caused conditions,[93] including asthma, and they have been shown to be especially pronounced in neurological conditions (including migraine and chronic pain).[94]

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”[8]:48 and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (American Psychiatric Association Diagnostic and Statistical Manual[95]) nor have they been listed among somatoform disorders in the International Classification of Diseases.[96]

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.[8]:17

Genetic[edit | edit source]

The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.[41]

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.[41] They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.[41][97][98]

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,[41][97][98][99][100][101] including polymorphisms and differences in expression of the following: CYP2D6, MTHFR, NAT1, NAT2, GSTM1, and PON1 and PON2.[102][103][104]

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.[41]

COVID-19 and Long COVID[edit | edit source]

There have been anecdotal reports of people with Long COVID, or chronic COVID, developing new allergies, including fragrance and other chemical sensitivities.[105]

ME/CFS and multiple chemical sensitivity[edit | edit source]

MCS has been called a common comorbidity of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) by several consensus documents:[106][107][108]

  1. The Canadian Consensus Criteria (2003) for ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
  2. The International Consensus Criteria (2011) for Myalgic Encephalomyelitis lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
  3. The U.S. ME/CFS Clinician Coalition publication Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) (2020) lists "chemical sensitivity" as a symptom of ME/CFS, and MCS as a comorbidity.[109]

ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.

Recognition[edit | edit source]

In 1996, an expert panel at WHO/ICPS (International Classification for Patient Safety) was set up to examine MCS.[110] The panel:

  1. "accepted the existence of a disease of unclear pathogenesis",
  2. proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
  3. suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.[110]

MCS is not included as a separate, discrete disease by the World Health Organization's (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:

  1. J68.9: unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
  2. T78.4: unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."[1]:139

In the ICD-10-DM and ICD-10-SGB-V, Germany's adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (Chemical-Sensitivity[MCS]-Syndrom, Multiple-) under the code T78.4; this is also in use in Austria.[111][1] Japan also recognizes MCS as a separate disease.[1]:139[112][7] And in some countries, like Sweden, chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).[9] In 2012, Denmark introduced code DR688A1 for Symptoms related to chemicals and scents (Symptomer relateret til dufte og kemiske stoffer fra SKS), in the Medically Unexplained Symptoms, under R68.8 Other specified general symptoms and signs.[37]

And as mentioned above, chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. Centers for Disease Control and Prevention (CDC) said that ME/CFS patients can have sensitivities to chemicals.[113]

Treatment[edit | edit source]

Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.[1] Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.[114][115]

There is no clinically proven cure for MCS.[8][112] There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."[7][8][16][23][112]

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.[7][116]

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.[6][112] Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.[6][112][117]

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,[115] likely because of oxidative stress or because neural inflammation has reduced blood flow.[115][118][119][120] Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.[115] The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).[114]

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were:

  • face masks (with HEPA and VOC filters)
  • portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters), and
  • water purifiers.[114]

In Australia in 2021 there will be an observational trial of MCS patients using Nimodipine, a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

Accessibility needs[edit | edit source]

“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”[121]

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.[8][20][122][39][123][124][125][126][127][128][129][130][131][132][133] The most influential of these may be the indoor air quality policy of the the U.S. Centers for Disease Control and Prevention (CDC), which says:

  1. "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"[21]
  2. "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
  3. "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."[21]

Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.[134][135][136][137][138][139][140][141][142][143][144][145][146] The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."[20]:30 With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."[147]

Hospital care[edit | edit source]

Hospitals with fragrance-free policies are common Canada and Sweden.[39][20][8][123][124][125][126][127][128][129][130][131][132][133] Canadian examples include:

  • Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."[124]
  • Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."[125]

As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.[148][149][150][151][117][152][153][154][155][156]

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.[152][117][156][155] As well, some individual hospitals have their own policies for MCS patients.[149][157]

Housing[edit | edit source]

People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.[158][159][160][161][162][163]:12

A 2002 housing survey of people with MCS in the United States found that:

  • 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
  • 25% had lived in a car (nine months average)
  • 15% had lived in a tent (eight months average)
  • 73% of respondents had lived in a house that made them sick
  • 47% said they were spending more than they could afford on accessible housing
  • 43% said their current housing was neither accessible nor permanent.[159]

While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.[160]

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.[161]

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".[162] Some of these included:

People with MCS suffer as a result of their lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.[163] The inquiry concluded that in society at large, there was little recognition of how serious and severe environmental illness could be and that there was "a discouraging shortage of services and supports" for people living with conditions like MCS.[163] It also found that people with environmental illness commonly experienced stigma, including from landlords, who were "often skeptical about the severity and impact of their conditions.”[163]:7,12,19

History[edit | edit source]

In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.[7][110]

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.[7][110]

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in The Archives of Environmental Health in 1999.[1][5]

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.[110]

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the Italian Consensus on MCS.[164] This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

Controversy[edit | edit source]

MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the reality of the illness.[165] This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.[166][167][168][169][170][171][172][173] These efforts have created a perception that MCS is a controversial or disputed condition,[9][174] which is not supported by recent academic reviews of MCS research.[3][8][1][6][99]

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.[175]

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.[169][176][177][178][179][180][181] Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.[182][183][184][185][186][187][188][189][190][191][177][174]

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia[192][170][193] (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”[194][193]); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."[41]

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,[175] their commentaries are at odds with: (1) the current medical consensus about MCS,[1][5][6][8][16]:31[2][43]:11 (2) conclusions of the most recent academic reviews of MCS research in scientific journals,[1][6] and (3) the recognition of the condition by the WHO/ICPS[110] and by other national and state health agencies, physicians' organizations and hospitals.[1][7][21][16]:17[112][117][153][149][154][152][156][43]:11[121][195][196]

In the media[edit | edit source]

Safe (1995)[edit | edit source]

Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film Safe. The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.[197] In the film he explores stigma, alienation and isolation.

Safe is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.[198]

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.[197] While Haynes said Carol’s isolation was both the answer and the problem for her.[198]

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.[199].

Afflicted docuseries (2018)[edit | edit source]

Netflix's 2018 documentary series Afflicted features several patients with MCS.

After its release, Afflicted was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.[166]

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said unethical journalistic methods were used in the making of the series and called for it to be taken off Netflix.[200]

Notable studies and publications[edit | edit source]

  • 1987, Cullen, M.R. The worker with multiple chemical sensitivities: An overview[201] - (Abstract)
Defines the Cullen criteria
  • 1999, Multiple chemical sensitivity: a 1999 consensus[5] - (Full text)
  • 2005, Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition[26] - (Abstract)
Defines the Lacour criteria. Based on the 1987 Cullen criteria.
  • 2014, Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity[44] (Full text)
  • 2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity[202] - (Full text)
  • 2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives[1] - (Full text)
  • 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review[6] - (Abstract)
  • 2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)[164] - (Full text - English)
Original title: Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS - (Full text - Italian)
  • 2019, International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products[136] - (Full text)
  • 2021, Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity[40] - (Full text)
  • 2021, Mast cell activation may explain many cases of chemical intolerance[45] (Full text)
  • 2021, Multiple Chemical Sensitivity[203] (Full text)

News articles and interviews[edit | edit source]

Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia's occupational health and safety regulator Workplace OHS says on its website that it is in the employers' best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers' health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”.
An intolerance to manufactured scents can lead to migraines, respiratory issues and long-term sick leave. So should they be banned in public spaces?

See also[edit | edit source]

Learn more[edit | edit source]

References[edit | edit source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 Rossi, Sabrina; Pitidis, Alessio (February 2018). "Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives". Journal of Occupational and Environmental Medicine. 60 (2): 138–146. doi:10.1097/JOM.0000000000001215. ISSN 1076-2752. PMC 5794238. PMID 29111991. ...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Grouppo di Italiano Studio MCS (May 23, 2019). "2. Epidemiologia" [2. Epidemiology] (PDF). Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS [Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]. Università degli Studi di Milano, Italy.
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Grouppo di Italiano Studio MCS (May 23, 2019). "1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso" [1. Clinical features of the disease]. Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS [Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS] (PDF). Università degli Studi di Milano, Italy.
  4. 4.0 4.1 Grouppo di Italiano Studio MCS (May 23, 2019), "1.2 Scatenamento della MCS" [1.2 Triggering of MCS], Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS [Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS] (PDF), Università degli Studi di Milano, Italy
  5. 5.0 5.1 5.2 5.3 5.4 5.5 5.6 "Multiple chemical sensitivity: a 1999 consensus". Arch. Environ. Health. 54 (3): 147–9. 1999. doi:10.1080/00039899909602251. PMID 10444033.
  6. 6.0 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 Viziano, A.; Micarelli, A.; Pasquantonio, G.; Della-Morte, D.; Alessandrini, M. (November 2018). "Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review". Int Arch Occup Environ Health. 91 (8): 923–935. doi:10.1007/s00420-018-1346-z. PMID 30088144.
  7. 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 National Industrial Chemicals Notification and Assessment Scheme; Office of Chemical Safety and Environmental Health (2010). A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs. Canberra, Australia. ISBN 978-0-9807221-4-7. Archived from the original on November 2010. Recognition of MCS as a disease and disability...In Germany, MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, Austria has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10
  8. 8.00 8.01 8.02 8.03 8.04 8.05 8.06 8.07 8.08 8.09 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 Task Force on Environmental Health (2017), Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. (PDF), Toronto, Ontario: Ministry of Health and Long-Term Care
  9. 9.0 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9 Steinemann, Anne (March 2018). "National Prevalence and Effects of Multiple Chemical Sensitivities". Journal of Occupational and Environmental Medicine. 60 (3): e152–e156. doi:10.1097/JOM.0000000000001272. ISSN 1076-2752. PMC 5865484. PMID 29329146.
  10. Loria-Kohen, Viviana; Marcos-Pasero, Helena; de la Iglesia, Rocío; Aguilar-Aguilar, Elena; Espinosa-Salinas, Isabel; Herranz, Jesús; Ramírez de Molina, Ana; Reglero, Guillermo (August 22, 2017). "Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients". Medicina Clinica. 149 (4): 141–146. doi:10.1016/j.medcli.2017.01.022. ISSN 1578-8989. PMID 28283271.
  11. Gibson, Pamela Reed; Leaf, Britney; Komisarcik, Victoria (January 12, 2016). "Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness". Journal of Nursing Education and Practice. 6 (5): 75. doi:10.5430/jnep.v6n5p75. ISSN 1925-4059.
  12. García-Sierra, Rosa; Álvarez-Moleiro, María (July 1, 2014). "Evaluation of suffering in individuals with multiple chemical sensitivity". Clínica y Salud. 25 (2): 95–103. doi:10.1016/j.clysa.2014.06.006. ISSN 1130-5274.
  13. Alobid, Isam; Nogué, Santiago; Izquierdo-Dominguez, Adriana; Centellas, Silvia; Bernal-Sprekelsen, Manuel; Mullol, Joaquim (December 1, 2014). "Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell". European Archives of Oto-Rhino-Laryngology. 271 (12): 3203–3208. doi:10.1007/s00405-014-3015-5. ISSN 1434-4726.
  14. 14.0 14.1 14.2 Gibson, PR; Vogel, VM (January 2009). "Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity". J Clin Nurs. 18 (1): 72–81. doi:10.1111/j.1365-2702.2008.02439.x.
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