Multiple chemical sensitivity (MCS), also known as idiopathic environmental intolerances (IEI), is a disputed chronic condition characterized by symptoms that the affected person attributes to low-level exposures to commonly used chemicals. Symptoms are typically vague and non-specific. They may include fatigue, headaches, nausea, and dizziness.
Commonly attributed substances include scented products, pesticides, plastics, synthetic fabrics, smoke, petroleum products, and paint fumes.
Although the symptoms themselves are real, and can be disabling, MCS is not recognized as an organic, chemical-caused illness by the World Health Organization, American Medical Association, or any of several other professional medical organizations. Blinded clinical trials show that people with MCS react as often and as strongly to placebos as they do to chemical stimuli; the existence and severity of symptoms is related to perception that a chemical stimulus is present. Some attribute the symptoms to depression, somatoform disorders, or anxiety disorders.
Commonly attributed substances include scented products, pesticides, plastics, synthetic fabrics, smoke, petroleum products, and paint fumes.
Although the symptoms themselves are real, and can be disabling, MCS is not recognized as an organic, chemical-caused illness by the World Health Organization, American Medical Association, or any of several other professional medical organizations. Blinded clinical trials show that people with MCS react as often and as strongly to placebos as they do to chemical stimuli; the existence and severity of symptoms is related to perception that a chemical stimulus is present. Some attribute the symptoms to depression, somatoform disorders, or anxiety disorders.
Signs and symptoms
Symptoms are common, but vague and non-specific for the condition. The most common are feeling tired, "brain fog" (short-term memory problems, difficulty concentrating), gastrointestinal problems, headaches, and muscle pain.
A partial list of other symptoms patients have attributed to MCS include: difficulty breathing, pains in the throat, chest, or abdominal region, skin irritation, headaches, neurological symptoms (nerve pain, pins and needles feelings, weakness, trembling, restless leg syndrome), tendonitis, seizures, visual disturbances (blurring, halo effect, inability to focus), anxiety, panic and/or anger, sleep disturbance, suppression of immune system, digestive difficulties, nausea, indigestion/heartburn, vomiting, diarrhea, joint pains, vertigo/dizziness, abnormally acute sense of smell (hyperosmia), sensitivity to natural plant fragrance or natural pine terpenes, dry mouth, dry eyes, and an overactive bladder.
Causes
There is no clear consensus for the cause or causes of the symptoms of MCS. A 2007 National Institute of Environmental Health Sciences paper defined MCS as a "chronic, recurring disease caused by a person's inability to tolerate an environmental chemical or class of foreign chemicals".In addition to extreme sensitivity to low concentrations of certain chemicals, several hypotheses have been proposed. The distinction between physiological and psychological causes is often difficult to test, and it is particularly challenging for MCS because many substances used to test for sensitivity have a strong odor. Odor cues make double blind studies of MCS patients difficult, as scents can provoke a psychosomatic response or recall expectations and prior beliefs. People with an MCS diagnosis show no differences in symptom severity, blood pressure, or heart rate when exposed to clean air or to solvents at a concentration too low to smell.
Chemical triggers
Many chemicals have been reported to trigger MCS symptoms. Substances with strong scents are the most commonly reported triggers. These include a variety of cleaning agents, pesticides, perfumes, vehicle exhaust, the products used in barber shops and beauty salons, new carpeting, new furniture, chlorine and fluoride in drinking water, fresh ink, and less commonly wood smoke and secondhand tobacco smoke. Food items reported as triggers include tartrazine (a.k.a. FD&C Yellow #5 or E102), and other azo dyes (in the absence of an allergy), caffeine, and monosodium glutamate.Immune
One proposed hypothesis for the cause of multiple chemical sensitivity is immune system dysfunction after being sensitized by a chemical exposure.Psychological
Several mechanisms for a psychological etiology have been proposed, including theories based on misdiagnoses of an underlying mental illness, stress, or classical conditioning. Many people with MCS meet the criteria for major depressive disorder or anxiety disorder. Other proposed explanations include somatoform disorder, panic disorder, migraine, chronic fatigue syndrome, or fibromyalgia, where symptoms such as brain fog and headaches can be triggered by chemicals or inhalants. Through behavioral conditioning, they may develop real, but unintentionally psychologically produced, symptoms such as anticipatory nausea when they encounter certain odors or other perceived triggers. Affected individuals may also have a tendency to "catastrophically misinterpret benign physical symptoms" or simply have a disturbingly acute sense of smell. The personality trait absorption, in which individuals are predisposed to becoming deeply immersed in sensory experiences, may be stronger in individuals reporting symptoms of MCS. Behaviors exhibited by MCS sufferers may reflect broader sociological fears about industrial pollution and broader societal trends of technophobia and chemophobia.Neurological
People who suffer from MCS may have a neurological dysfunction in the odor-processing areas of the brain or may respond strongly to fumes or scents for some other reason.Genetic differences in metabolism
Genetic differences relating to toxicant metabolism pathways, such as polymorphisms and differences in expression in CYP2D6, NAT2, GSTM1, and PON1 and PON2, have been proposed as a cause for differences in susceptibility to MCS. Elevated nitric oxide and peroxynitrite (NO/ONOO-) could then cause the symptoms of MCS and several related conditions, including fibromyalgia, posttraumatic stress disorder, Gulf War syndrome, and chronic fatigue syndrome.Gulf War syndrome
People with British Gulf War syndrome who used personal organophosphate pesticides may be more likely to report the symptoms of MCS.Diagnosis
No characteristically unique signs, laboratory test abnormalities, tissue pathology, or course of illness have been identified, and it remains unclear whether symptoms are physiologically or psychologically generated.International Classification of Diseases
The International Statistical Classification of Diseases and Related Health Problems (ICD), maintained by the World Health Organization, does not recognize multiple chemical sensitivity or environmental sensitivity as a valid diagnosis. The Australian Department of Health recognizes that sometimes debilitating symptoms are attributed to MCS but notes that diagnosis, treatment, and any underlying mechanism remain uncertain. The German Institute for Medical Documentation and Information recognizes MCS as a physical disease and is subsequentially recognized in Austria. The American Medical Association does not recognize MCS as an organic disease because of the lack of scientific evidence supporting a cause-and-effect relationship between very low level exposure and the symptoms of MCS. The American Academy of Allergy, Asthma, and Immunology, the California Medical Association, the American College of Physicians, and the International Society of Regulatory Toxicology and Pharmacology also do not recognize MCS. The US Occupational Safety and Health Administration (OSHA) indicates that MCS is highly controversial and that there is insufficient scientific evidence to explain the relationship between the suggested causes of MCS and its symptoms. OSHA recommends evaluation by a physician knowledgeable of the symptoms presented.Other
In response to a WHO call for papers at the 5th Paris Appeal Congress of Environmental Idiopathic Intolerance conference that took place in Belgium on 18 May 2015, a report that was generally supportive quoted a number of international practitioners. This was provisionally accepted by the Spanish health ministry, and later found proven by a judge in the case of a plumber in the Province of Castellón.MCS is a diagnosis of exclusion, and the first step in diagnosing a potential MCS sufferer is to identify and treat all other conditions which are present and which often explain the reported symptoms. For example, depression, allergy, thyroid disorders, orthostatic syndromes, lupus, hypercalcemia, and anxiety need to be carefully evaluated and, if present, properly treated. The "gold standard" procedure for identifying a person who has MCS is to test response to the random introduction of chemicals the patient has self-identified as relevant. This may be done in a carefully designed challenge booth to eliminate the possibility of contaminants in the room. Chemicals and controls, sometimes called prompts, are introduced in a random method, usually scent-masked. The test subject does not know when a prompt is being given. Objective and subjective responses are measured. Objective measures, such as the galvanic skin response, indicate psychological arousal, such as fear, anxiety, or anger. Subjective responses include patient self-reports. A diagnosis of MCS can only be justified when the subject cannot consciously distinguish between chemicals and controls, and when responses are consistently present with exposure to chemicals and consistently absent when prompted by a control.
A 1999 consensus statement recommends that MCS be diagnosed according to six standardized criteria:
- Symptoms are reproducible with repeated (chemical) exposures
- The condition has persisted for a significant period of time
- Low levels of exposure (lower than previously or commonly tolerated) result in manifestations of the syndrome (i.e. increased sensitivity)
- The symptoms improve or resolve completely when the triggering chemicals are removed
- Responses often occur to multiple chemically unrelated substances
- Symptoms involve multiple-organ symptoms (runny nose, itchy eyes, headache, scratchy throat, ear ache, scalp pain, mental confusion or sleepiness, palpitations of the heart, upset stomach, nausea and/or diarrhea, abdominal cramping, aching joints).
Treatment
In various studies, about one half of the patients who seek medical treatment for symptoms of MCS meet the criteria for depressive and anxiety disorders. Because many people eliminate whole categories of food in an effort to reduce symptoms, a complete review of the patient's diet may be needed to avoid nutritional deficiencies.Epidemiology
Epidemiological data from three states put the prevalence of chemical sensitivity in 1999 at 16 to 33% of the general population, 2 to 6% of whom have already been diagnosed with MCS.[45] Women complain of MCS significantly more often than men, and most patients are 30 to 50 years old at time of diagnosis.Gulf War syndrome
Several clinical and epidemiological studies conducted in the United States and in the United Kingdom have investigated the occurrence of MCS in military personnel deployed to the Persian Gulf during the 1990s. Some of the health complaints and symptoms reported by veterans of the Gulf War 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.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. 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.
The odds of reporting MCS or chronic multiple-symptom illness was 3.5 times greater for Gulf War veterans than non-Gulf veterans.
Gulf War veterans have an increased rate of multiple-symptom conditions compared to military personnel deployed to other conflicts, and although it is unexplained, Gulf War syndrome is not considered distinct from other medically unexplained syndromes observed in civilian populations, including MCS.
History
MCS was first proposed as a distinct disease by 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, clinical ecology emerged as a non-recognized medical specialty. In 1984, the Society for Clinical Ecology changed its name to American Academy of Environmental Medicine (AAEM). In the 1990s, an association was noted with chronic fatigue syndrome, fibromyalgia, and Gulf War syndrome.In 1994, the AMA, American Lung Association, US EPA and US Consumer Product Safety Commission published a booklet on 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.
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 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.
In 1997, U.S. Social Security Administration Commissioner John Callahan issued a court memorandum officially recognizing MCS "as a medically determinable impairment" on an agency-wide basis. That is, without making any statement about the cause of MCS or the role of chemicals in MCS, the Social Security administration agrees that some MCS patients are too disabled to be meaningfully employed.
A 1997 U.S. court decision held that MCS "is untested, speculative, and far from generally accepted in the medical or toxicological community," and thus cannot be used as the basis for disability claims. Furthermore, accommodations sought for MCS are sometimes denied as being unreasonable as a matter of law.
In July 2017, the Task Force on Environmental Health of the Ontario, Canada Ministry of Health and Long-Term Care issued a Phase 1 report, "Time for Leadership: Recognizing and Improving Care for those with ME/CFS, FM and ES/MCS", summarized in Canadian Family Physician in June 2018 (v.64{6}; PMC5999262), "Recent Insights Into 3 Under-recognized Conditions: Myalgic Encephalomyelitis–Chronic Fatigue Syndrome, Fibromyalgia, and Environmental Sensitivities–Multiple Chemical Sensitivity". "[M]ounting evidence of biological mechanisms" is cited in the latter. In February 2018, the Journal of Occupational and Environmental Medicine (official publication of the American College of Occupational and Environmental Medicine) published "Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" covering seventeen years of literature internationally on the topic.
