Multiple chemical sensitivity: Potential role for neural sensitization

An emerging issue in environmental health is the phenomenon of multiple che mical sensitivity (MCS). Multiple chemical sensitivity is a controversial d isorder characterized by multiorgan symptoms in response to low-level chemi cal exposures that are considered safe for the general population. The onse t of MCS is often attributed to prior repeated chemical exposures in the ho me and/or workplace, and, once initiated, symptoms are triggered by extreme ly low levels of many chemicals/foods. No single case definition exists for MCS due to several issues that call into question its validity as a distin ct illness induced by prior chemical exposure. Hypotheses regarding the eti ological basis for MCS range from direct toxicological effects of chemicals to the notion that MCS is purely a psychological "belief system". One lead ing hypothesis suggests that MCS represents a neural sensitization phenomen on, wherein susceptible individuals demonstrate extreme sensitivity to chem icals and odor intolerance due to central nervous system (CNS) sensitizatio n processes. The recent development of an animal model for MCS provides som e support for the sensitization hypothesis and may offer evidence for behav ioral changes observed in at least a subset of those reporting MCS.