Editing Multiple chemical sensitivity (section)

== 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>