Multiple chemical sensitivity

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Multiple chemical sensitivity (MCS), also known as idiopathic environmental intolerances (IEI), is an unrecognized and controversial diagnosis characterized by chronic

Commonly attributed substances include scented products (e.g. perfumes), pesticides, plastics, synthetic fabrics, smoke, petroleum products, and paint fumes.^[1]

Symptoms

Symptoms are typically

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.[5]

Symptoms mainly arise from the autonomic nervous system (such as nausea or dizziness) or have psychiatric or psychological aspects (such as difficulty concentrating).^[6]

Possible causes

Various different causes for MCS have been hypothesized.^[7]

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. Various health care professionals and government agencies are working on giving those who report the symptoms proper care while searching for a cause.^[8]

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.^[9] "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."^[9]

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.^[10]

Immunological

Researchers have studied immunity biomarkers 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 cytokines, but this phenomenon is not specific to MCS and overall there is no evidence that low-level chemical exposure causes an immune response.^[7]

Genetic

It has been hypothesized that there is a heritable

Gaétan Carrier and colleagues write that the genetic hypothesis appears implausible when the evidence around it is judged by the Bradford Hill criteria.^[7]

Psychological

This section needs more primary sources. Please review the contents of the section and add the appropriate references if you can. Unsourced or poorly sourced material may be challenged and removed. Find sources: "Multiple chemical sensitivity" – news · newspapers · books · scholar · JSTOR (November 2021)

Several mechanisms for a psychological etiology of the condition have been proposed, including theories based on misdiagnoses of an underlying mental illness, stress, or

These theories have attracted criticism.[8]^[19]

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.^{[20][needs update]}

A 2018 systematic review concluded that the evidence suggests that abnormalities in sensory processing pathways combined with peculiar personality traits best explains this condition.^[21]

Diagnosis

In practice, diagnosis relies entirely upon the self-reported claim that symptoms are triggered by exposure to various substances.^[22]

Many other tests have been promoted by various people over the years, including testing of the immune system,

The stress and anxiety experienced by people reporting MCS symptoms are significant.^[22] Neuropsychological assessments do not find differences between people reporting MCS symptoms and other people in areas such as verbal learning, memory functioning, or psychomotor performance.^[22] Neuropsychological tests are sensitive but not specific, and they identify differences that may be caused by unrelated medical, neurological, or neuropsychological conditions.^[22]

Another major goal for diagnostic work is to identify and treat any other medical conditions the person may have.

Different researchers and proponents use different definitions, which complicates research and can affect diagnosis.[23] For example, the 1987 definition that requires symptoms to begin suddenly after an identifiable, documented exposure to a chemical,^[24] but the 1996 definition by the WHO/ICPS says that the cause can be anything, including other medical conditions or psychological factors.^[24][25]

In 1996, an expert panel at WHO/ICPS was set up to examine MCS.^[26] 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 what they renamed idiopathic environmental intolerances (IEI):

1. the disease was acquired (not present from birth) and must produce multiple relapsing symptoms;
2. the symptoms must be closely related to "multiple environmental influences, which are well tolerated by the majority of the population"; and
3. it could not be explained by any other medical condition.^[26]

In Japan, MCS is called chemical hypersensitivity or chemical intolerance (化学物質過敏症; 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.

There is no single proven treatment for MCS.[8] The goal of treatment is to improve quality of life, with fewer distressing symptoms and the ability to maintain employment and social relationships, rather than to produce a permanent cure.^[22]

A

Common self-care strategies include avoiding exposure to known triggers and emotional self-care.^[22] 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.^[22] 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.^[22] 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.^[22] Treatments that have not been scientifically validated, such as detoxification, have been used by MCS patients. Unproven treatments can be expensive, may cause side effects, and may be counterproductive.^[22]

Epidemiology

Prevalence rates for MCS vary according to the diagnostic criteria used.^[29] The condition is reported across industrialized countries and it affects women more than men.^[8]: 37

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.^[30] They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.^[30]

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 [31]}

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 per cent reported having adverse reactions to multiple chemicals.^[32][33][34] The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.^[33]

Gulf War syndrome

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.^[35]

A population-based, cross-sectional epidemiological study involving American veterans of the Gulf War, non-Gulf War veterans, and non-deployed reservists enlisted both during Gulf War era and outside the Gulf War era concluded the prevalence of MCS-type symptoms in Gulf War veterans was somewhat higher than in non-Gulf War veterans.^[36] After adjusting for potentially confounding factors (age, sex, and military training), there was a robust association between individuals with MCS-type symptoms and psychiatric treatment (either therapy or medication) before deployment and, therefore, before any possible deployment-connected chemical exposures.^[36]

The odds of reporting MCS or chronic multiple-symptom illness was 3.5 times greater for Gulf War veterans than non-Gulf veterans.^[37] Gulf War veterans have an increased rate of being diagnosed with multiple-symptom conditions compared to military personnel deployed to other conflicts.^[38]

Prognosis

About half of those who claim to be affected by MCS get better over the course of several years, while about half continue to experience distressing symptoms.^[22]

History

MCS was first proposed as a distinct disease by

Since the 1950s, many hypotheses have been advanced for the science surrounding multiple chemical sensitivity.[7]

In the 1990s, an association was noted with chronic fatigue syndrome, fibromyalgia, and Gulf War syndrome.^[39]

In 1994, the AMA,

The different understandings of MCS over the years have also resulted in different proposals for names.[25] 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,^[23] while another researcher, whose definition includes people with allergies and acute poisoning, calls it chemical sensitivity.^{[25][clarification needed]}

See also

• 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

References