Multiple Chemical Sensitivity (MCS) Disorder is a highly controversial issue. However, MCS is not an "allergy," but it is often confused with skin allergies, food allergies or nasal allergies.
In theory, MCS is an adverse physical reaction to low levels of some common chemicals. Chemical sensitivity is generally accepted as a reaction to chemicals but debate continues on whether MCS is classifiable as an illness. There are a number of synonyms for MCS, including "20th century disease," "environmental illness," "idiopathic environmental illness" and "chemical AIDS."
Proposed theories to explain the cause of MCS include dysfunction of the immune system (but not overreaction of the immune system, such as allergy), neurobiological sensitization, and various psychological theories. There is insufficient scientific evidence to confirm a relationship between any of these possible causes and symptoms. Due to the lack of definite information an evaluation must be performed by a physician knowledgeable of the symptoms of this condition.
SOURCE: This information should not substitute for seeking responsible, professional medical care. Adapted with permission from the U.S. Department of Labor, Occupational Safety and Health Administration http://www.osha.gov/SLTC/multiplechemicalsensitivities/index.html