multiple chemical sensitivity

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Multiple Chemical Sensitivity



Multiple chemical sensitivity—also known as MCS syndrome, environmental illness, idiopathic environmental intolerance, chemical AIDS, total allergy syndrome, or simply MCS—is a disorder in which a person develops symptoms from exposure to chemicals in the environment. With each incidence of exposure, lower levels of the chemical will trigger a reaction and the person becomes increasingly vulnerable to reactions triggered by other chemicals.
Medical experts disagree on the cause of the syndrome, and as to whether MCS is a clinically recognized illness. In a 1992 position statement that remained unchanged as of early 2000, the American Medical Association's Council on Scientific Affairs did not recognize MCS as a clinical condition due to a lack of accepted diagnostic criteria and controlled studies on the disorder. A more recent discussion of methodological problems in published studies of MCS, as well as recommendations for patient care, may be found in the 1999 position paper on MCS drafted by the American College of Occupational and Environmental Medicine (ACOEM). As of 2003, however, many researchers in Europe as well as the United States regard MCS as a contemporary version of neurasthenia, a concept first introduced by a physician named George Miller Beard in 1869.


Multiple chemical sensitivity typically begins with one high-dose exposure to a chemical, but it may also develop with long-term exposure to a low level of a chemical. Chemicals most often connected with MCS include: formaldehyde; pesticides; solvents; petrochemical fuels such as diesel, gasoline, and kerosene; waxes, detergents, and cleaning products; latex; tobacco smoke; perfumes and fragrances; and artificial colors, flavors, and preservatives. People who develop MCS are commonly exposed in one of the following situations: on the job as an industrial worker; residing or working in a poorly ventilated building; or living in conditions of high air or water pollution. Others may be exposed in unique incidents.
Because MCS is difficult to diagnose, estimates vary as to what percentage of the population develops MCS. However, most MCS patients are female. The median age of MCS patients is 40 years old, and most experienced symptoms before they were 30 years old. There is also a large percentage of Persian Gulf War veterans who have reported symptoms of chemical sensitivity since their return from the Gulf in the early 1990s.

Causes and symptoms

Chemical exposure is often a result of indoor air pollution. Buildings that are tightly sealed for energy conservation may cause a related illness called sick building syndrome, in which people develop symptoms from chronic exposure to airborne environmental chemicals such as formaldehyde from the furniture, carpet glues, and latex caulking. A person moving into a newly constructed building, which has not had time to degas, may experience the initial high-dose exposure that leads to MCS.
As of late 2002, the specific biochemical and physiological mechanisms in humans that lead to MCS are not well understood. A recent hypothesis, however, suggests that MCS is the end result of four different mechanisms of sensitization acting to reinforce one another. Further research is required to test this hypothesis.
The symptoms of MCS vary from person to person and are not chemical-specific. Symptoms are not limited to one physiological system, but primarily affect the respiratory and nervous systems. Symptoms commonly reported are headache, fatigue, weakness, difficulty concentrating, short-term memory loss, dizziness, irritability and depression, itching, numbness, burning sensation, congestion, sore throat, hoarseness, shortness of breath, cough, and stomach pains.
One commonly reported symptom of MCS is a heightened sensitivity to odors, including a stronger emotional reaction to them. A Japanese study published in late 2002 reported that patients diagnosed with MCS can identify common odors as accurately as most people, but regard a greater number of them as unpleasant.
One test that has been devised to evaluate patients with MCS is the capsaicin inhalation test. Capsaicin is an alkaloid found in hot peppers that is sometimes used in topical creams and rubs for the treatment of arthritis. When inhaled, capsaicin causes coughing in healthy persons as well as those with allergies that affect the airway; however, persons with MCS cough more deeply and frequently than control subjects when given a dose of capsaicin. Although the test is not diagnostic in the strict sense, it has been shown to be an effective way of identifying patients with MCS.


Multiple chemical sensitivity is a twentieth-century disorder, becoming more prevalent as more human-made chemicals are introduced into the environment in greater quantities. It is especially difficult to diagnose because it presents no consistent or measurable set of symptoms and has no single diagnostic test or marker. For example, a 2002 study of PET scans of MCS patients found no significant functional changes in the patients' brain tissues. Physicians are often either unaware of MCS as a condition, or refuse to accept that MCS exists. They may be unable to diagnose it, or may misdiagnose it as another degenerative disease, or may label it as a psychosomatic illness (a physical illness that is caused by emotional problems). Their lack of understanding generates frustration, anxiety, and distrust in patients already struggling with MCS. However, a new specialty of medicine is evolving to address MCS and related illnesses: occupational and environmental medicine. A physician looking for MCS will take a complete patient history and try to identify chemical exposures.
Some MCS patients may be helped by a psychologic evaluation, particularly if they show signs of panic attacks or other anxiety disorders. It is known that many patients with MCS suffer from comorbid depression and anxiety. In addition, MCS patients appear to have high rates of mood disorders compared to asthma patients as well as normal test subjects.


While doctors may recommend antihistamines, analgesics, and other medications to combat the symptoms, the most effective treatment is to avoid those chemicals which trigger the symptoms. This becomes increasingly difficult as the number of offending chemicals increases, and people with MCS often remain at home where they are able to control the chemicals in their environment. This isolation often limits their abilities to work and socialize, so supportive counseling may also be appropriate.

Alternative treatment

Some MCS patients find relief with detoxification programs of exercise and sweating, and chelation of heavy metals. Others support their health with nutritional regimens and immunotherapy vaccines. Some undergo food-allergy testing and testing for accumulated pesticides in the body to learn more about their condition and what chemicals to avoid. Homeopathy and acupuncture can give added support to any treatment program for MCS patients. Botanical medicine canhelptosupport theliver andother involved organs.


Once MCS sets in, sensitivity continues to increase and a person's health continues to deteriorate. Strictly avoiding exposure to triggering chemicals for a year or more may improve health.


Multiple chemical sensitivity is difficult to prevent because even at high-dose exposures, different people react differently. Ensuring adequate ventilation in situations with potential for acute high-dose or chronic low-dose chemical exposure, as well as wearing the proper protective equipment in industrial situations, will minimize the risk.

Key terms

Capsaicin — An alkaloid found in hot peppers that is used in an inhalation test to identify patients with MCS.
Degas — To release and vent gases. New building materials often give off gases and odors and the air should be well circulated to remove them.
Neurasthenia — A term coined in the late nineteenth century to refer to a condition of chronic mental and physical weakness and fatigue. Some researchers regard MCS as a twentieth-century version of neurasthenia.
Sick building syndrome — An illness related to MCS in which a person develops symptoms in response to chronic exposure to airborne environmental chemicals found in a tightly sealed building.



American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders. 4th ed., revised. Washington, DC: American Psychiatric Association, 2000.
Beers, Mark H., MD, and Robert Berkow, MD, editors. "Multiple Chemical Sensitivity Syndrome." Section 21, Chapter 287. In The Merck Manual of Diagnosis and Therapy. Whitehouse Station, NJ: Merck Research Laboratories, 2004.
Gibson, Pamela. Multiple Chemical Sensitivity: A Survival Guide. Oakland, CA: New Harbinger Publications, 2000.


Bornschein, S., C. Hausteiner, A. Drzezga, et al. "PET in Patients With Clear-Cut Multiple Chemical Sensitivity (MCS)." Nuklearmedizin 41 (December 2002): 233-239.
Bornschein, S., C. Hausteiner, T. Zilker, and H. Forstl. "Psychiatric and Somatic Disorders and Multiple Chemical Sensitivity (MCS) in 264 'Environmental Patients'." Psychological Medicine 32 (November 2002): 1387-1394.
Caccappollo-vanVliet, E., K. Kelly-McNeil, B. Natelson, et al. "Anxiety Sensitivity and Depression in Multiple Chemical Sensitivities and Asthma." Journal of Occupational and Environmental Medicine 44 (October 2002): 890-901.
Johansson, A., O. Lowhagen, E. Millqvist, and M. Bende. "Capsaicin Inhalation Test for Identification of Sensory Hyperreactivity." Respiratory Medicine 96 (September 2002): 731-735.
Ojima, M., H. Tonori, T. Sato, et al. "Odor Perception in Patients with Multiple Chemical Sensitivity." Tohoku Journal of Experimental Medicine 198 (November 2002): 163-173.
Pall, M. L. "NMDA Sensitization and Stimulation by Peroxynitrite, Nitric Oxide, and Organic Solvents as the Mechanism of Chemical Sensitivity in Multiple Chemical Sensitivity." FASEB Journal 16 (September 2002): 1407-1417.
Schafer, M. L. "On the History of the Concept Neurasthenia and Its Modern Variants Chronic-Fatigue-Syndrome, Fibromyalgia and Multiple Chemical Sensitivities" [in German] Fortschritte der Neurologie-Psychiatrie 70 (November 2002): 570-582.
Ternesten-Hasseus, E., M. Bende, and E. Millqvist. "Increased Capsaicin Cough Sensitivity in Patients with Multiple Chemical Sensitivity." Journal of Occupational and Environmental Medicine 44 (November 2002): 1012-1017.


American Academy of Environmental Medicine. P.O. Box CN 1001-8001, New Hope, PA 18938. (215) 862-4544.
American College of Occupational and Environmental Medicine (ACOEM). 1114 North Arlington Heights Road, Arlington Heights, IL 60004. (847) 818-1800.


"Multiple Chemical Sensitivities: Idiopathic Environmental Intolerance." Position Statement by the American College of Occupational and Environmental Medicine (ACOEM), April 26, 1999.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.

mul·ti·ple chem·i·cal sen·si·tiv·i·ty

a symptom array of variable presentation attributed to recurrent exposure to known environmental chemicals at dosages generally below levels established as harmful; complaints involve multiple organ systems.
Farlex Partner Medical Dictionary © Farlex 2012

id·i·o·path·ic en·vir·on·men·tal in·tol·er·ance

(IEI) (id'ē-ō'path-ik en-vī'rŏn-men'tăl in-tol'ĕr-ăns)
A puzzling condition in which nonspecific symptoms involving many organ systems arise by unknown mechanisms after putative environmental exposures to very low levels of diverse chemicals.
Synonym(s): multiple chemical sensitivity.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

mul·ti·ple chem·i·cal sen·si·ti·vi·ty

(mŭl'ti-pĕl kem'i-kăl sen'si-tiv'i-tē)
Symptom array of variable presentation attributed to recurrent exposure to known environmental chemicals at dosages generally below levels established as harmful.
Medical Dictionary for the Dental Professions © Farlex 2012
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