Multiple Chemical Sensitivity (MCS)
MCS is an acquired condition characterized by more or less severe symptomatic reactions in a wide variety of organ systems, to low levels of common ambient toxicants. Symptoms for people with MCS can be triggered by exposure to doses of chemicals at levels to which most people do not normally react. Some may react to residues of commonly used herbicides and persistent insecticides used in drinking water and shower water, as well as to pesticide residues found on and in supermarket foods.
Reactions can include: mild and sudden fatigue, sharp metallic taste in the mouth or other unusual paraestersias, nausea, severe skin rashes, headaches and brain fog, intense migraines, disabling cerebral dysfunction, loss of consciousness, and life-threatening asthma.
MCS is an acquired condition through one large exposure or by a long accumulation of lesser exposures to chemicals which eventually reach a critical mass in their tissues.
Estimates of MCS prevalence vary from four percent to 34 percent of the general population (N. Ashford and C.S. Miller, Chemical Exposures: Low Levels, High Stakes, 2nd ed., p. 332-33). Slightly more than four percent of the population has been formally diagnosed with MCS by an MD, whereas 30 to 40% report they are often make sick in some way from exposure to chemicals such as pesticides, diesel exhaust and artificial fragrances (Thomas Kerns, Environmentally Induced Illnesses, p. 53, 2001).
Ashford and Miller hypothesize that "lower levels of toxic substances could be more damaging than higher levels, perhaps because damage from the former is so slight that usual cell repair mechanisms are not triggered and the damage becomes permanent.