Multiple chemical sensitivity

Multiple chemical sensitivities, also known as environmental intolerances, is a poorly understood and often disputed syndrome which is described using the following criteria:

• The symptoms are reproducible with repeated chemical exposure;
• the condition is chronic;
• low levels of exposure (lower than previously tolerated) result in manifestations of the syndrome;
• the symptoms improve or resolve when the incitants are removed;
• responses occur to multiple chemically unrelated substances; and
• symptoms involve multiple organ systems.

Epidemiology

(in progress)

Genetic basis

People diagnosed using the 1999 consensus statement criteria have significant differences in some drug-metabolizing enzymes and other enzymes involved in detoxication. These findings, which require replication, point to an unequivocal somatic and toxic basis to multiple chemical sensitivities.

Immunological basis

In a case control study involving 417 persons (223 cases, 194 controls), lymphocyte count was found to be consistent low in victims of MCS.

The TILT theory of environmental diseases

Claudia Miller of the University of Texas points out that the term multiple chemical sensisitivities erroneously suggests that the MCS patient is only intolerant to so-called "chemicals", while the evidence rather suggests that people with MCS react as well to very low levels of common food ingredients, such as xanthines and, for example, alcohol.

The Toxicant-Induced Loss of Tolerance (TILT) model describes more closely MCS by specifying that, in this syndrome, there is a generalized loss of tolerance to many unrelated and otherwise benign molecules, and that this loss of tolerance is indeed due to an exposure to toxics (or "toxicants").