Editing Multiple chemical sensitivity

{{Short description|Controversial medical diagnosis}}
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<!--Definition and symptoms-->
'''Multiple chemical sensitivity''' ('''MCS''') is an unrecognized and controversial diagnosis characterized by chronic [[symptoms]] attributed to exposure to low levels of commonly used chemicals.<ref name="Genuis2013">{{Cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology?|journal=Clinical Therapeutics|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291}}</ref><ref name="Templeton">{{Citation |last1=Templeton |first1=Douglas M. |last2=Schwenk |first2=Michael |last3= Duffus |first3=John H. |date=2016 |title=Multiple Chemical Sensitivity (MCS) |work=[[International Union of Pure and Applied Chemistry|IUPAC]] Glossary of Terms Used in Neurotoxicology |publisher=[[De Gruyter]] |url=https://www.researchgate.net/publication/286049129 |doi=10.1515/pac-2015-0103 |quote=multiple chemical sensitivity (MCS) -environmental illness -idiopathic environmental intolerance -Intolerance condition attributed to extreme sensitivity of individuals to various environmental chemicals, found in air, food, water, building materials, or fabrics. Note 1:  This syndrome is characterized by the patient's belief that his or her symptoms are caused by very low-level exposure to environmental chemicals. The term "chemical" is used to refer broadly to many natural and man-made substances, some of which have several chemical constituents. Note 2: ... }}</ref> Symptoms are typically [[vagueness|vague]] and [[non-specific symptoms|non-specific]]. They may include [[fatigue (medical)|fatigue]], [[headache]]s, [[nausea]], and [[dizziness]]. 

<!--Cause and diagnosis-->
Recent imaging studies have shown that it is likely a [[Neurology|neurological]] condition.<ref>{{Cite journal |last1=Molot |first1=John |last2=Sears |first2=Margaret |last3=Anisman |first3=Hymie |date=2023-08-01 |title=Multiple chemical sensitivity: It's time to catch up to the science |journal=Neuroscience & Biobehavioral Reviews |volume=151 |page=105227 |doi=10.1016/j.neubiorev.2023.105227 |pmid=37172924 |issn=0149-7634|doi-access=free }}</ref>

<!--Management and prognosis-->
MCS is a [[chronic disease]] that requires ongoing management.  In the long term, about half of people with MCS get better and about half continue to be affected, sometimes severely.<ref name="Current 2021" />
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== Classification ==
In [[nosological]] terms, MCS may be more than one disease.<ref name="Linde">{{Cite book |last1=Linde |first1=Brian |url=https://onlinelibrary.wiley.com/doi/book/10.1002/0471435139 |title=Patty's Industrial Hygiene |last2=Redlich |first2=Carrie A. |date=10 February 2021 |publisher=Wiley |isbn=978-0-471-29784-0 |editor-last=Harris |editor-first=Robert |edition=7th |language=en |chapter=Symptomatic Responses to Low-Level Occupational and Environmental Exposures |doi=10.1002/0471435139.hyg013.pub3 |via=<!-- available in [[WP:TWL]] -->}}</ref><ref name="Current 2021" />

It is generally considered a subtype of non-allergic [[chemical intolerance]] (also called ''chemical sensitivity'').<ref name="Linde2">{{Cite book |last1=Linde |first1=Brian |url=https://onlinelibrary.wiley.com/doi/book/10.1002/0471435139 |title=Patty's Industrial Hygiene |last2=Redlich |first2=Carrie A. |date=10 February 2021 |publisher=Wiley |isbn=978-0-471-29784-0 |editor-last=Harris |editor-first=Robert |edition=7th |language=en |chapter=Symptomatic Responses to Low-Level Occupational and Environmental Exposures |doi=10.1002/0471435139.hyg013.pub3 |via=<!-- available in [[WP:TWL]] -->}}</ref>

MCS is considered an [[acquired disorder]], meaning that it was not present from birth but instead developed later.<ref name="Linde" />

Compared to other conditions with [[medically unexplained physical symptoms]], such as [[Myalgic encephalomyelitis/chronic fatigue syndrome]], [[fibromyalgia]] or [[Gulf War syndrome]], MCS symptoms are only present in response to environmental triggers.<ref name="Linde" />

=== Name ===
The name ''multiple chemical sensitivity'' has been criticized, partly because MCS is not a [[Hypersensitivity|sensitivity]] in the [[allergic]] or immunological meaning of that word.<ref name="Linde">{{Cite book |last1=Linde |first1=Brian |url=https://onlinelibrary.wiley.com/doi/book/10.1002/0471435139 |title=Patty's Industrial Hygiene |last2=Redlich |first2=Carrie A. |date=10 February 2021 |publisher=Wiley |isbn=978-0-471-29784-0 |editor-last=Harris |editor-first=Robert |edition=7th |language=en |chapter=Symptomatic Responses to Low-Level Occupational and Environmental Exposures |doi=10.1002/0471435139.hyg013.pub3 |via=<!-- available in [[WP:TWL]] -->}}</ref>  Being more sensitive than average to some chemical exposures (e.g., [[secondhand smoke]]) is fairly common.<ref name="Linde" />  MCS is generally used to refer to more significant disability.<ref name="Linde" />

The name has also been criticized because it suggests that chemical exposure is the actual cause or [[etiology]], which has not been proven.  The word ''chemical'' in the name is used loosely and includes natural substances (e.g., the aromas produced by pine trees or other fragrant plants).<ref name="Templeton" />  Other names, such as [[idiopathic environmental intolerance]], have been recommended as more accurate alternatives.<ref name="Linde" />

=== Definitions ===
Different researchers and proponents use different definitions, which complicates research and can affect diagnosis.<ref name="International Programme">{{Cite web |last=International Programme on Chemical Sensitivity |date=February 1996 |title=Report of Multiple Chemical Sensitivities Workshop |url=https://apps.who.int/iris/bitstream/handle/10665/63109/PCS_96.29.pdf |access-date=11 June 2020 |location=Berlin, Germany}}</ref>{{Obsolete source|reason=[[WP:MEDRS]] prefers sources within the last 5 years or so|date=May 2024}} For example, the 1987 definition that requires symptoms to begin suddenly after an identifiable, documented exposure to a chemical,<ref name="Rossi">{{Cite journal |last1=Rossi |first1=Sabrina |last2=Pitidis |first2=Alessio |date=February 2018 |title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives |journal=Journal of Occupational and Environmental Medicine |language=en-US |volume=60 |issue=2 |pages=138–146 |doi=10.1097/JOM.0000000000001215 |issn=1076-2752 |pmc=5794238 |pmid=29111991}}</ref> but the 1996 definition by the WHO/ICPS says that the cause can be anything, including other medical conditions or psychological factors.<ref name="Rossi" /><ref name=":1">{{Cite journal |last=Katoh |first=Takahiko |date=2018 |title=Multiple Chemical Sensitivity (MCS): History, Epidemiology and Mechanism |trans-title=Multiple Chemical Sensitivity (MCS): History, Epidemiology and Mechanism |journal=Nihon Eiseigaku Zasshi (Japanese Journal of Hygiene) |language=ja |volume=73 |issue=1 |pages=1–8 |doi=10.1265/jjh.73.1 |issn=1882-6482 |pmid=29386440 |doi-access=free}}</ref>

In 1996, an expert panel at WHO/ICPS was set up to examine MCS.<ref name="Schwenk">{{Cite journal |last1=Schwenk |first1=Michael |date=2004 |title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects |journal=GMS Current Topics in Otorhinolaryngology, Head and Neck Surgery |volume=3 |pages=Doc05 |issn=1865-1011 |pmc=3199799 |pmid=22073047}}</ref>{{Obsolete source|reason=[[WP:MEDRS]] prefers sources within the last 5 years or so|date=May 2024}} The panel accepted the existence of "a disease of unclear pathogenesis", rejected the claim that MCS was caused by chemical exposure, and proposed these three diagnostic requirements for a group of conditions that includes MCS, which they called ''idiopathic environmental intolerances'' (IEI):

# the disease was acquired (not present from birth) and must produce multiple relapsing symptoms;
#the symptoms must be closely related to "multiple environmental influences, which are well tolerated by the majority of the population"; and
#it [[Diagnosis of exclusion|could not be explained by any other]] medical condition.<ref name="Schwenk" />{{Obsolete source|reason=[[WP:MEDRS]] prefers sources within the last 5 years or so|date=May 2024}}
In Japan, MCS is called ''chemical hypersensitivity'' or ''chemical intolerance'' (<span lang="ja" dir="ltr">化学物質過敏症</span>; kagaku bushitsu kabinsho), and the 1999 Japanese definition requires one or more of four major symptoms – headaches; malaise and fatigue; muscle pain; joint pain – combined with laboratory findings and/or some minor symptoms, such as mental effects or skin conditions.<ref name=":1a">{{Cite web |title=Safety and Health Topics: Multiple Chemical Sensitivities |url=https://www.osha.gov/multiple-chemical-sensitivities |access-date=2021-01-06 |publisher=Occupational Safety and Health Administration}}</ref> The defined lab findings are abnormalities in [[Parasympathetic nervous system|parasympathetic nerves]], [[Cerebral cortex|cerebral cortical]] dysfunction diagnosed by [[SPECT]] testing, [[visuospatial]] abnormalities, abnormalities of [[Eye movement disorder|eye movement]], or a positive [[provocation test]].<ref name=":1" />

Another definition requires a known precipitating event (e.g., an injury or an illness) followed by the appearance of multi-organ symptoms that predictably wax and wane in response to a variety of exposures that do not bother other people.<ref name="Current 2021">{{Cite book |last=Harrison |first=Robert J. |title=Current Occupational & Environmental Medicine |publisher=McGraw-Hill Education/Medical |year=2021 |isbn=978-1-260-14343-0 |edition=Sixth |location=New York |pages=853–860 |chapter=Multiple Chemical Sensitivity |oclc=1250024967}}</ref> For example, this could describe someone who always feels sick after using ordinary household cleaning products, when exposed to [[new car smell]], or having a live [[Christmas tree]] in the house, and then feels better again when not around these things.  Additionally, the symptoms cannot be explainable through other conditions that can be identified with ordinary [[medical tests]], such as an [[allergic reaction]].<ref name="Current 2021" />

== Symptoms ==
Symptoms are typically [[Vagueness|vague]] and [[Non-specific symptoms|non-specific]], such as [[Fatigue (medical)|fatigue]] or [[headache]]s.<ref name="Canberra">{{Citation|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs |date=2010 |publisher= National Industrial Chemicals Notification and Assessment Scheme, Australian Government |location=Canberra, Australia |url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp |archive-url=https://web.archive.org/web/20200307155500/http://test.nicnas.gov.au/Media/Latest_News/MCS.asp |archive-date=2020-03-07 }}</ref> These symptoms, although they can be disabling, are called non-specific because they are not associated with any single specific medical condition.

Symptoms affect a variety of different [[Organ system|organ systems]].  Different people have different symptoms and different affected systems, but cognitive and neurologic symptoms (e.g., headache and [[brain fog]]) are common, as are [[Systemic symptom|systemic symptoms]] (e.g., fatigue).<ref name="Linde" />  Other people have symptoms affecting the eyes, ears, and nose (e.g., [[stuffy nose]]), the respiratory system (e.g., [[shortness of breath]]), gastrointestinal system (e.g., [[nausea]]), musculoskeletal system (e.g., [[joint pain]]), or dermatological system (e.g., [[itching]]).<ref name="Linde" />

A 2010 review of MCS literature said that the following symptoms, in this order, were the most reported in the condition: headache, fatigue, confusion, depression, shortness of breath, arthralgia, myalgia, nausea, dizziness, memory problems, gastrointestinal symptoms, respiratory symptoms.<ref name="Canberra" />

Symptoms mainly arise from the [[autonomic nervous system]] (such as [[nausea]] or [[dizziness]]) or have psychiatric or psychological aspects (such as difficulty concentrating).<ref name="Katoh">{{Cite journal |last=Katoh |first=Takahiko |date=2018 |title=Multiple Chemical Sensitivity (MCS): History, Epidemiology and Mechanism |journal=Nihon Eiseigaku Zasshi |trans-journal=Japanese Journal of Hygiene |language=ja|volume=73|issue=1|pages=1–8|doi=10.1265/jjh.73.1|issn=1882-6482|pmid=29386440|doi-access=free}}</ref>

== Possible causes ==
Various different causes for MCS have been hypothesized, including [[immunological]], [[toxicological]], and [[neurobiological]] ideas.<ref name="Templeton" /><ref name=quebec-synth>{{Cite book |language=fr-ca |title=Syndrome de sensibilité chimique multiple, une approche intégrative pour identifier les mécanismes physiopathologiques |date=June 2021 |url=https://www.inspq.qc.ca/sites/default/files/publications/2729-syndrome-sensibilite-chimique-synthese.pdf |publisher=Institut national de santé publique du Québec |type=Synthèse |isbn=978-2-550-88675-4 |vauthors=Carrier G, Tremblay M, Allard R}}</ref>

There is a general agreement among most MCS researchers that the cause is not specifically related to sensitivity to chemicals, but this does not preclude the possibility that symptoms are caused by other known or unknown factors.<ref name="Templeton" /><ref name="Toronto">{{Citation|work=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|location= Toronto, Ontario |publisher= Ministry of Health and Long-Term Care}}</ref> Various health care professionals and government agencies are working on giving those who report the symptoms proper care while searching for a cause.<ref name="Toronto"/>

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">{{Citation|work=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|location= Toronto, Ontario |publisher= Ministry of Health and Long-Term Care |page=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" />

The US [[Occupational Safety and Health Administration]] (OSHA) says that MCS is highly controversial and that there is insufficient scientific evidence to explain the relationship between any of the suggested causes of MCS – it lists "allergy, dysfunction of the immune system, neurobiological sensitization, and various psychological theories" as the suggested causes – and its symptoms.<ref>{{cite web|title=Safety and Health Topics &#124; Multiple Chemical Sensitivities|url=http://www.osha.gov/SLTC/multiplechemicalsensitivities/index.html|access-date=2014-06-08|publisher=Osha.gov}}</ref>

=== Immunological ===
Researchers have studied immunity [[biomarker]]s in people with MCS to determine whether MCS could be an autoimmune disorder or allergic response, but the results have been inconclusive. Some people with MCS appear to have excess production of [[inflammatory cytokine]]s, but this phenomenon is not specific to MCS and overall there is no evidence that low-level chemical exposure causes an immune response.<ref name=quebec-synth/>

=== Genetic ===
It has been hypothesized that there is a heritable [[genetic trait]] which pre-disposes people to be hypersensitive to low-level chemical exposure and so develop MCS. To investigate, researchers compared the [[genotype|genetic makeup]] of people with MCS, to people without. The results were generally inconclusive and contradictory, thus failing to support the hypothesis.<ref name=quebec-synth/>

Gaétan Carrier and colleagues write that the genetic hypothesis appears implausible when the evidence around it is judged by the [[Bradford Hill criteria]].<ref name=quebec-synth/>

=== Psychological ===
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A 2018 systematic review concluded that the evidence suggests that abnormalities in sensory processing pathways combined with peculiar personality traits best explains this condition.<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. |url=https://www.researchgate.net/publication/326880068 |journal=Int Arch Occup Environ Health |volume=91 |issue=8 |pages=923–935 |doi=10.1007/s00420-018-1346-z |pmid=30088144 |bibcode=2018IAOEH..91..923V |s2cid=51936485}}</ref>

== Diagnosis ==
{{One source|section|find=multiple chemical sensitivity diagnosis|date=October 2024}}
In practice, diagnosis relies entirely upon the [[Self-report study|self-reported]] claim that the symptoms are triggered by exposure to various substances.<ref name="Current">{{Cite book|title=Current Occupational & Environmental Medicine|last=Harrison|first=Robert|publisher=McGraw-Hill Education/Medical|year=2014|isbn=978-0-07-180816-3|edition=Fifth|location=New York|pages=819–826|chapter=Multiple Chemical Sensitivity|oclc=898477589|url=https://archive.org/details/currentoccupatio0000unse_c5n1|quote=controversial methods have been used ... including elimination or rotary diversified diets, vitamins or nutritional supplements, oxygen, antifungal and antiviral agents, thyroid hormone supplement, supplemental estrogen or testosterone, transfer factor, chemical detoxification through exercise and sauna treatment, intravenous gamma-globulin, and intracutaneous or subcutaneous neutralization. A specially designed chemical-free environmental control unit has been used as a method to decrease blood pesticide levels and ... Controversial treatment methods offer hope of improvement to many individuals with MCS, and some patients do report symptom improvement over time. Many ... are expensive and rarely are covered by health insurance. These treatment methods have not been validated through carefully designed, controlled trials, may have unwanted side effects ... page 826}}</ref> Commonly attributed substances include scented products (e.g. perfumes), [[pesticide]]s, plastics, synthetic fabrics, smoke, [[petroleum]] products, and paint fumes.<ref name="Genuis2013" />

Many other tests have been promoted by various people over the years, including testing of the immune system, [[porphyrin metabolism]], provocation-neutralization testing, [[autoantibodies]], the [[Epstein–Barr virus]], testing for evidence of exposure to pesticides or heavy metals, and challenges involving exposure to chemicals, foods, or inhalants.<ref name="Current" /> None of these tests correlate with MCS symptoms, and none are useful for diagnosing MCS.<ref name="Current" />

The stress and [[Anxiety disorder|anxiety]] experienced by people reporting MCS symptoms are significant.<ref name="Current" /> [[Neuropsychological assessment]]s do not find differences between people reporting MCS symptoms and other people in areas such as verbal learning, memory functioning, or [[psychomotor learning|psychomotor performance]].<ref name="Current" /> Neuropsychological tests are [[Sensitivity and specificity|sensitive but not specific]], and they identify differences that may be caused by unrelated medical, neurological, or neuropsychological conditions.<ref name="Current" />

Another major goal for diagnostic work is to identify and treat any other medical conditions the person may have.<ref name="Current" /> People reporting MCS-like symptoms may have other health issues, ranging from common conditions, such as [[Depression (mood)|depression]] or [[asthma]], to less common circumstances, such a documented chemical exposure during a [[work accident]].<ref name="Current" /> These other conditions may or may not have any relationship to MCS symptoms, but they should be diagnosed and treated appropriately, whenever the [[patient history]], [[physical examination]], or routine [[medical test]]s indicates their presence.<ref name="Current" /> The [[differential diagnosis]] list includes [[solvent exposure]], [[occupational asthma]], and allergies.<ref name="Current" />

==Management==
There is no single proven treatment for MCS<ref name="Toronto" /> and no scientific consensus on supportive therapies.<ref name="Toronto" />{{Rp|17}}<ref name="Canberra"/> The literature generally agrees on the need for MCS patients to avoid the specific substances that trigger reactions for them as well as [[xenobiotic]]s in general, in order to prevent further sensitization.<ref name="Toronto" />{{Rp|17}}<ref name="Canberra"/> The goal of treatment is to improve [[Quality of life (healthcare)|quality of life]], with fewer distressing symptoms and the ability to maintain employment and social relationships, rather than to produce a permanent cure.<ref name="Current" />

Some literature recommends a [[multidisciplinary]] treatment approach that takes into account the uncommon personality traits often seen in affected individuals and physiological abnormalities in sensory pathways and the limbic system.<ref name="pmid30088144" />

Common [[self-care]] strategies include avoiding exposure to known triggers and emotional self-care.<ref name="Current" /> Healthcare providers can provide useful education on the body's natural ability to eliminate and excrete toxins on its own and support positive self-care efforts.<ref name="Current" /> Avoiding triggers, such as by removing smelly cleaning products from the home, can reduce symptoms and increase the person's sense of being able to reclaim a reasonably normal life.<ref name="Current" /> However, for other people with MCS, their efforts to avoid suspected triggers will backfire, and instead produce harmful emotional side effects that interfere with the overall goal of reducing distress and disability.<ref name="Current 2021" /> Treatments that have not been scientifically validated, such as "elimination or rotary diversified diets", hormone supplement and chemical detoxification through [[exercise]] have been used by people with MCS. "Controversial treatment methods offer hope of improvement to many individuals with MCS.<ref name="Current" />" Unproven treatments can be expensive, may cause side effects, and may be counterproductive.<ref name="Current" />

Various combinations of different antioxidants together with "detoxifying" measures that are not evidence based are recommended by some authors. "Treatment with a multitude of pills and infusions may lead to "catastrophizing", thus making patients perceive their disorder particularly negatively; this phenomenon is known to have a negative impact on the subsequent disease course ... such treatments place a significant financial strain on patients."<ref name="pmid32026633">{{cite journal |vauthors=Harter K, Hammel G, Fleming M, Traidl-Hoffmann C |title=Multiple chemical sensitivity (MCS) - a guide for dermatologists on how to manage affected individuals |journal=J Dtsch Dermatol Ges |volume=18 |issue=2 |pages=119–130 |date=February 2020 |pmid=32026633 |doi=10.1111/ddg.14027|doi-access=free }}</ref>

== Epidemiology ==
Prevalence rates for MCS vary according to the diagnostic criteria used.<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. http://test.nicnas.gov.au/Media/Latest_News/MCS.asp {{Webarchive|url=https://web.archive.org/web/20200307155500/http://test.nicnas.gov.au/Media/Latest_News/MCS.asp |date=2020-03-07 }}</ref> For example, a 2014 study estimated that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name="Toronto" />{{Rp|37}}  A 2018 study found that 6.5% of Australian adults reported having a medical diagnosis of MCS.<ref>Pigatto PD, Guzzi G. Prevalence and Risk Factors for MCS in Australia. ''Preventive Medicine Reports'' 2019.</ref><ref name=":21">{{Cite news |date=2 July 2018 |title=Common chemical products making Australians sick, study finds |url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds |access-date=20 November 2019 |work=The University of Melbourne Newsroom}}</ref><ref name=":0">{{cite journal |author=Steinemann A |year=2018 |title=Prevalence and effects of multiple chemical sensitivities in Australia |journal=Prev Med Rep |volume=10 |pages=191–4 |doi=10.1016/j.pmedr.2018.03.007 |pmc=5984225 |pmid=29868366 |doi-access=free}}</ref>  In Germany, 9% of adults say they have MCS, and 12% of adults in the US say they have been diagnosed.<ref name="Current 2021" />  When self-reports are included, about 20% of Australians and 25% of Americans say that they are more sensitive to chemicals than average.<ref name=":0" /><ref name="Current 2021" />  {{As of|2022}}, the number of people with MCS has either plateaued or is declining.<ref>{{Cite book |last1=Gardiner |first1=Kerry |url=https://onlinelibrary.wiley.com/doi/book/10.1002/9781119887638 |title=Pocket Consultant: Occupational Health |last2=Rees |first2=David |last3=Adisesh |first3=Anil |last4=Zalk |first4=David |last5=Harrington |first5=Malcolm |last6=Gervais |first6=Roxane |last7=Saary |first7=Joan |date=2022-03-25 |publisher=Wiley |isbn=978-1-119-71861-1 |edition=1 |language=en |doi=10.1002/9781119887638.ch18}}</ref>
[[File:Pareto_principle.svg|thumb|Women are far more likely to have MCS.<ref name="Current 2021" />]]
The condition is reported across industrialized countries.<ref name="Toronto" />{{Rp|37}} It affects significantly more women than men.<ref name="Current 2021" />  A typical age of onset is near [[middle age]].<ref name="Current 2021" />  People with MCS are more likely to have high [[socioeconomic status]] and to be well educated.<ref name="Current 2021" />  They are also more likely to have stressful work situations and a history of subjective health complaints.<ref name="Current 2021" />

For about half of people with MCS, the symptoms could be considered disabling.<ref name=":21" /><ref name=":0" />

===Related syndromes===
Symptoms attributed to [[Gulf War syndrome]] are similar to those reported for MCS, including headache, fatigue, muscle stiffness, joint pain, inability to concentrate, sleep problems, and gastrointestinal issues.<ref name="Current 2021" />  Gulf War veterans are somewhat more likely to have symptoms consistent with MCS.<ref name="Current 2021" /> 

MCS is also similar to [[sick building syndrome]], with both showing non-specific symptoms such as headaches, respiratory irritation and fatigue.<ref name="Current 2021" />  There is also some overlap in symptoms between MCS and [[myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS), though chemical exposures are not suspected in ME/CFS.<ref name="Current 2021" />

== Prognosis ==
About half of those with MCS get better over the course of several years, while about half continue to experience distressing or disabling symptoms.<ref name="Current 2021" />

== History ==
MCS was first proposed as a distinct disease by [[Theron Randolph|Theron G. Randolph]] in 1950. In 1965, Randolph founded the [[Society for Clinical Ecology]] as an organization to promote his ideas about symptoms reported by his patients. As a consequence of his insistence upon his own, non-standard definition of ''allergy'' and his unusual theories about how the immune system and toxins affect people, the ideas he promoted were widely rejected, and [[clinical ecology]] emerged as a non-recognized medical specialty.<ref name="Current" />

Since the 1950s, many hypotheses have been advanced for the science surrounding multiple chemical sensitivity.<ref name=quebec-synth/>

In the 1990s, an association was noted with chronic fatigue syndrome, fibromyalgia, and Gulf War syndrome.<ref name="Donnay">{{cite journal|author=Donnay|first=Albert H|date=1999|title=On the Recognition of Multiple Chemical Sensitivity in Medical Literature and Government Policy|journal=International Journal of Toxicology|volume=18|issue=6|pages=383–392|doi=10.1080/109158199225099|s2cid=72141513}}</ref>

In 1994, the AMA, [[American Lung Association]], [[United States Environmental Protection Agency|US EPA]] and the US [[Consumer Product Safety Commission]] published a booklet on [[Indoor air quality|indoor air pollution]] that discusses MCS, among other issues. The booklet further states that a pathogenesis of MCS has not been definitively proven, and that symptoms that have been self-diagnosed by a patient as related to MCS could actually be related to allergies or have a psychological basis, and recommends that physicians should counsel patients seeking relief from their symptoms that they may benefit from consultation with specialists in these fields.<ref name="urlIndoor Air Pollution: An Introduction for Health Professionals | Publications | Indoor Air | Air | US EPA">{{cite book|title=Indoor Air Pollution: An Introduction for Health Professionals|year=1994|publisher= Co-sponsored by: The American Lung Association (ALA), The Environmental Protection Agency (EPA), The Consumer Product Safety Commission (CPSC), and The American Medical Association (AMA)|url=http://www.epa.gov/iedweb00/pubs/hpguide.html#faq1|quote=[D]efinition of the phenomenon is elusive and its pathogenesis as a distinct entity is not confirmed....The current consensus is that in cases of claimed or suspected MCS, complaints should not be dismissed as psychogenic, and a thorough workup is essential. Primary care givers should determine that the individual does not have an underlying physiological problem and should consider the value of consultation with allergists and other specialists.|access-date=2008-06-30}}</ref>

In 1995, an Interagency Workgroup on Multiple Chemical Sensitivity was formed under the supervision of the Environmental Health Policy Committee within the [[United States Department of Health and Human Services]] to examine the body of research that had been conducted on MCS to that date. The work group included representatives from the [[Centers for Disease Control and Prevention]], [[United States Environmental Protection Agency]], [[United States Department of Energy]], [[Agency for Toxic Substances and Disease Registry]], and the [[National Institutes of Health]]. The Predecisional Draft document generated by the workgroup in 1998 recommended additional research in the basic epidemiology of MCS, the performance of case-comparison and challenge studies, and the development of a case definition for MCS. However, the workgroup also concluded that it was unlikely that MCS would receive extensive financial resources from federal agencies because of budgetary constraints and the allocation of funds to other, extensively overlapping syndromes with [[medically unexplained symptoms|unknown cause]], such as chronic fatigue syndrome, fibromyalgia, and Gulf War syndrome. The Environmental Health Policy Committee is currently inactive, and the workgroup document has not been finalized.<ref>{{citation|last=Interagency Workgroup on Multiple Chemical Sensitivity|title=A Report on Multiple Chemical Sensitivity (MCS)|date=1998-08-24|url=http://web.health.gov/environment/mcs/|archive-url=https://web.archive.org/web/20140718033446/http://www.health.gov/environment/mcs/toc.htm|publisher=Web.health.gov|access-date=2014-06-08|archive-date=2014-07-18}}</ref>

The different understandings of MCS over the years have also resulted in different proposals for names.<ref name=":1" /> For example, in 1996 the International Programme on Chemical Safety proposed calling it ''idiopathic environmental illness'', because of their belief that chemical exposure may not the sole cause,<ref name="International Programme" /> while another researcher, whose definition includes people with allergies and acute poisoning, calls it ''chemical sensitivity''.<ref name=":1" />

== Society and culture ==
Memoirs about multiple chemical sensitivity tend to follow a predictable pattern, with a description of various toxins and their effects alongside requests for others to help the writers by changing their behavior (e.g., by not wearing perfume).<ref name="Hsu">{{Citation |last=Hsu |first=Hsuan L. |title="Every Crime Has Its Peculiar Odor": Detection, Deodorization, and Intoxication |date=2020-12-31 |work=The Smell of Risk |pages=27–55 |url=https://www.degruyter.com/document/doi/10.18574/nyu/9781479807215.003.0002/html |publisher=New York University Press |doi=10.18574/nyu/9781479807215.003.0002 |isbn=978-1-4798-0537-2 |via=[[De Gruyter]]|url-access=subscription }}</ref><ref name="Alaimo">{{Cite book |last=Alaimo |first=Stacy |title=Bodily Natures: Science, Environment, and the Material Self |publisher=[[Indiana University Press]] |year=2010 |isbn=978-0-253-22240-4 |location=Bloomington (Ind.) |chapter=Deviant Agents: The Science, Culture, and Politics of Multiple Chemical Sensitivity}}</ref>  Frequently the memoirs focus more on things than on people, with interpersonal relationships fading into the background as the writers describe the vigilance they apply to everyday life, such as holding their breath whenever a car drives by, or trying to guess whether nearby people are likely to be smoking or wearing perfumes.<ref name="Hsu" />

Multiple chemical sensitivity has been featured in the film [[Safe (1995 film)|''Safe'']], a 1995 fictional [[psychological horror]] film.<ref name="Alaimo" /><ref>{{Citation |first1=Stephen |last1=Tapert |title=Julianne Moore |date=2022-12-31 |work=Best Actress |pages=451–454 |url=https://www.degruyter.com/document/doi/10.36019/9781978809598-075/html |access-date=2024-05-15 |publisher=Rutgers University Press |doi=10.36019/9781978809598-075 |isbn=978-1-9788-0959-8|url-access=subscription }}</ref>

=== International Statistical Classification of Diseases ===
The [[International Statistical Classification of Diseases and Related Health Problems]] (ICD), maintained by the [[World Health Organization]], is a [[medical coding]] system used for [[medical billing]] and statistical purposes – not for deciding whether any person is sick, or whether any collection of symptoms constitutes a single disease.  However, this does not mean that people with MCS-related symptoms cannot be treated or billed for medical services.MCS was illegally, without a proper proposal, added to USA ICD10 medical diagnostic code system 2011-2016, then, it was removed. https://icd.codes/icd10cm/F459# The public health service in Germany permits healthcare providers to bill for MCS-related medical services under the ICD-10 code T78.4, which is for idiosyncratic reactions, classified under the heading T78, <span lang="de" dir="ltr">Unerwünschte Nebenwirkungen, anderenorts nicht klassifiziert</span> ("adverse reactions, not otherwise specified").<ref name="Harter">{{Cite journal |last1=Harter |first1=Katharina |last2=Hammel |first2=Gertrud |last3=Fleming |first3=Megan |last4=Traidl-Hoffmann |first4=Claudia |date=February 2020 |title=Multiple chemical sensitivity (MCS) – a guide for dermatologists on how to manage affected individuals |journal=JDDG: Journal der Deutschen Dermatologischen Gesellschaft |language=en |volume=18 |issue=2 |pages=119–130 |doi=10.1111/ddg.14027 |issn=1610-0379 |pmid=32026633 |doi-access=free}}</ref> Being able to get paid for medical services and collect statistics about unspecified, idiosyncratic reactions does not mean that MCS is recognized as a specific disease or that any particular cause has been defined by the German government. MCS is named in [[Evidence-based medicine|evidence-based]] ("S3") [[Medical guideline|guidelines]] for the management of patients with nonspecific, functional symptoms.<ref name="Harter" />

==See also==
* [[Hyperosmia]]
* [[Electromagnetic hypersensitivity]]
* [[Sick building syndrome]]
* [[Sensory processing disorder]]
* [[Sensory processing sensitivity]]
* [[List of questionable diseases]]
* [[Environmental health]]
* [[Environmental medicine]]
* [[Indoor air quality]]
* [[Sense of smell#Disorders]]
* [[Mast cell activation syndrome|Mast Cell Activation Syndrome]] 

== References ==
{{reflist}}

== Further reading ==
*{{cite journal |vauthors=Molot J, Sears M, Marshall LM, Bray RI |title=Neurological susceptibility to environmental exposures: pathophysiological mechanisms in neurodegeneration and multiple chemical sensitivity |journal=Rev Environ Health |volume=37 |issue=4 |pages=509–530 |date=December 2022 |pmid=34529912 |doi=10.1515/reveh-2021-0043 |bibcode=2022RvEH...37..509M |type=review}}
*{{cite journal |vauthors=Palmieri B, Corazzari V, Vadala' M, Vallelunga A, Morales-Medina JC, Iannitti T |title=The role of sensory and olfactory pathways in multiple chemical sensitivity |journal=Rev Environ Health |volume=36 |issue=3 |pages=319–326 |date=September 2021 |pmid=33070122 |doi=10.1515/reveh-2020-0058 |doi-access=free |bibcode=2021RvEH...36..319P }}

== External links ==
* [http://www.merckmanuals.com/professional/special_subjects/syndromes_of_uncertain_origin/multiple_chemical_sensitivity_syndrome.html Multiple Chemical Sensitivity Syndrome] at the [[Merck Manual]] Professional Edition

{{Authority control}}

{{DEFAULTSORT:Multiple chemical sensitivity}}
[[Category:Alternative diagnoses]]
[[Category:Ailments of unknown cause]]
[[Category:Sensitivities]]