The Great Debate  
Website Special 
Winter 2003

There is ongoing debate about how to define MCS. Naysayers define it as a
psychological problem. The definition contained in the latest edition of
Casarett & Doull's Toxicology: The Basic Science of Poisons, 6th Edition is
interesting as it reflects changes in how standard medicine looks at the

Casarett and Doull defines Multiple Chemical Sensitivity as follows:

"Multiple chemical sensitivity syndrome (MCS) has been associated with
chemical hypersensitivity. The disease associated with MCS is characterized by multiple subjective symptoms related to more than one system. Many mechanisms have been suggested to explain how chemicals cause these symptoms; however, there remains considerable controversy as to a cause-effect relationship.  Clinical ecologists, the major proponents of MCS, have focused on immunologic mechanisms to explain the etiology. They hypothesize that MCS occurs when chemical exposure sensitizes certain individuals, and, upon subsequent exposure to exceedingly small amounts of these or unrelated chemical, the individual exhibits an adverse response.  Controlled studies on the immunologic states of individuals with MCS have shown no alterations in their immune system or any indication that MCS results from impairment of the immunity, including inappropriate immune response to chemicals.  The search for a theoretical basis for MCS is now being focused on the nervous system. Two untested hypotheses have emerged.  The first involves a non-specific inflamatory response to low-level irritants known as "neurogenic inflamation." The second involves induction of lasting changes in limbic and neuronal activity (via kindling) that alter a broad spectrum of behavioural and physiologic functions. The reader is referred to a review by Sikolski and colleagues (1995) for details and references concerning MCS."