Editing Multiple chemical sensitivity (section)

== 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" />