Multiple chemical sensitivity
|Multiple chemical sensitivity|
|Classification and external resources|
Multiple chemical sensitivity (MCS) is a chronic medical condition characterized by symptoms that the affected person attributes to low-level chemical exposure. Commonly attributed substances include scented products, pesticides, plastics, synthetic fabrics, smoke, petroleum products, and paint fumes. Symptoms are often vague and non-specific, such as nausea, fatigue, dizziness and headaches, but also commonly include inflammation of skin, joints, gastrointestinal tract and airways.
The National Institute of Environmental Health Sciences defines MCS as a "chronic, recurring disease caused by a person's inability to tolerate an environmental chemical or class of foreign chemicals".
MCS is not recognized as an organic, chemical-caused illness by the World Health Organization, but is recognized by numerous government agencies in the USA and elsewhere including the EPA, American Lung Association,Consumer Product Safety Commission, and the American Medical Association. <43>  Blinded clinical trials have shown MCS patients react as often and as strongly to placebos as they do to chemical stimuli; existence and severity of symptoms is related to perception that a chemical stimulus is present. Depression, anxiety, somatoform disorder, and similar mental health conditions are commonly associated with reports of MCS. Regardless of the etiology, some people with severe symptoms are disabled as a result.
Signs and symptoms
Symptoms of MCS may be mild to disabling and may be physical or psychological in nature. They include any symptom disruptive to mental or physical wellness that the affected individual attributes to exposure to a chemical or scent.
By far the most common symptoms are vague, non-specific complaints: feeling tired, "brain fog" (short-term memory problems, difficulty concentrating) and muscle pain. These complaints may be present with a wide variety of medical conditions, from psychiatric conditions, such as major depressive disorder, to neurological conditions, such as orthostatic intolerance, to sleep disorders, high blood pressure, autoimmune diseases and cancer.
A partial list of other symptoms patients have attributed to MCS include: difficulty breathing, pains in the throat, chest, or abdominal region, asthma, skin irritation, contact dermatitis, hives or other forms of skin rash, headaches, neurological symptoms (nerve pain, pins and needles feelings, weakness, trembling, restless leg syndrome), tendonitis, seizures, visual disturbances (blurring, halo effect, inability to focus), extreme 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.
There is no clear consensus for the cause or causes of the symptoms of MCS. 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.
Many chemicals have been reported to trigger MCS symptoms. Substances with strong scents are the most common 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 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 Gasoline, asphalt, agricultural chemicals, dry cleaning fluid, formaldehyde, air fresheners, and highlighters are also sometimes reported.
Several mechanisms for 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. Sufferers 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.
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. British Gulf War syndrome sufferers who used personal organophosphate pesticides may be more likely to report the symptoms of MCS.
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. 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 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.
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.
- 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).
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, and these conditions must be treated when present. While patients may resist the potentially stigmatizing diagnosis of a mental health disorder, many MCS sufferers benefit strongly from lifestyle changes. 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.
Epidemiological data from three states puts the prevalence of chemical sensitivity at 16 to 33% of the general population, 2 to 6% of whom have already been diagnosed with MCS. Women complain of MCS significantly more often than men, and most patients are 30 to 50 years old at time of diagnosis.
Relationship to 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.
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 etiology, 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 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.
- Chemophobia, the fear of chemicals
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- Position statement from the American Academy of Allergy, Asthma, and Immunology
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- MCS America
- MCS-Aware ("The Charity for Environmental Illness")
- The Chemical Sensitivity Foundation
- Fragrance Allergies: A Sensory Assault (WebMD)