What Is Multiple Chemical Sensitivity?

Multiple chemical sensitivity (MCS) is the name given by some to a condition in which various symptoms reportedly appear after a person has been exposed to any of a wide range of chemicals. The exposure may occur as a major event, such as a chemical spill, or from long-term contact with low-levels of chemicals, such as in an office with poor ventilation. As a result of exposure, people with MCS develop sensitivity and have reactions to the chemicals even at levels most people can tolerate.

Other names for this condition are "environmental illness" and "sick building syndrome."

Is MCS a Real Disorder?

Many recognized medical groups and societies, including the CDC, the American Medical Association, and the American Academy of Allergy, Asthma and Immunology, do not consider MCS a distinct physical disorder. There are several reasons for this.

First, there is a lack of clinical evidence to support a physical cause for the symptoms. In addition, people with MCS do not develop antibodies in response to chemical exposure, as is the case with an immune system, or allergic, reaction. Further, people with MCS also have high rates of mental health disorders, including depression, anxiety, and somatoform disorders -- mental disorders that are expressed through physical symptoms. About 50% of people with MCS meet the criteria for depression and/or anxiety disorders. Much of the controversy, then, centers on whether the symptoms associated with MCS are caused by physical or psychological factors.

What Are the Symptoms of MCS?

People with MCS have reported a wide range of symptoms, including:

Headache
Fatigue
Dizziness
Nausea
Irritability
Confusion
Difficulty concentrating
Intolerance to heat or cold
Earache
Stuffy head or congestion
Itching
Sneezing
Sore throat
Memory problems
Breathing problems
Changes in heart rhythm
Chest pain
Muscle pain and/or stiffness
Bloating or gas
Diarrhea
Skin rash or hives
Mood changes
How Common Is MCS?

Many healthcare practitioners do not recognize MCS as a disorder and, therefore, do not make a diagnosis of MCS. For this reason, it is not possible to assess how many people actually suffer from MCS. One estimate suggests that 2%-10% of people suffer some disruption in their lives because of MCS, although other experts believe these estimates are too high. The U.S. Environmental Protection Agency reported that about one-third of people working in sealed buildings claimed to be sensitive to one or more common chemicals. More women than men claim to have MCS, and it appears to occur most often in people between the ages of 30 and 50 years.

What Causes MCS?

The cause of MCS is unknown. One theory suggests that chemicals traveling in the air enter the nose and affect an area of the brain called the limbic system. The limbic system plays a role in emotions, motivated behavior, and memory, which may make a person more sensitive to a chemical odor it previously encountered, a condition called cacosmia. However, this theory has not been proven.

Another theory suggests that the immune system is somehow damaged in people with MCS. Still another theory, called "toxic-induced loss of tolerance" (TILT), suggests that acute or chronic exposure to chemicals causes some susceptible people to lose their tolerance for chemicals they previously could tolerate. Again, there is little evidence to support this theory.

People with MCS identify many products as chemical triggers, including:

Tobacco smoke
Perfume
Traffic exhaust or gasoline fumes
Nail polish remover
Newspaper ink
Hair spray
Paint or paint thinner
Insecticides
Artificial colors, sweeteners, and preservatives in food
Adhesive tape
New carpet
Flame retardants on clothing and furniture (such as mattresses)
Felt tip pens
Chlorine in swimming pools
How Is MCS Diagnosed?

There are no tests to diagnose MCS. A doctor generally bases his or her diagnosis on the person's description of symptoms, usually following a complete medical history and physical examination. The doctor may use diagnostic tests, such as X-rays and blood tests, to rule out true allergies and other physical or mental health disorders as the cause of the symptoms.

How Is MCS Treated?

Approaches to treatment vary. Most healthcare providers recommend avoiding the chemicals or foods that seem to trigger reactions. Some providers refer people with MCS to psychiatrists or psychologists, mental health professionals specially trained to diagnose and treat mental health disorders.

In most cases, the best course of action is for the person to stay in regular contact with a trusted healthcare provider. Within this doctor-patient relationship, the doctor can monitor the symptoms and stay alert to any changes. The doctor's main approach is likely to focus on reassuring and supporting the person, and preventing unnecessary tests and treatments. It may be necessary, however, to treat some of the symptoms, such as headaches or pain.

Can MCS Be Prevented?

Because little is known about the cause of MCS symptoms, it is not known if the disorder can be prevented.

Reviewed by the doctors at The Cleveland Clinic Department of Pulmonary, Allergy and Critical Care Medicine.

Edited by Charlotte E. Grayson, MD, Feb. 2004, WebMD.

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