Multiple Chemical Sensitivity; in broad terms it means an unusually severe sensitivity or allergy-like reaction to many different kinds of pollutants including solvents, VOC's (Volatile Organic Compounds), perfumes, petrol, diesel, smoke, "chemicals" in general and often encompasses problems with regard to pollen, house dust mites, and pet fur & dander. Multiple chemical sensitivity unlike true allergies - where the underlying mechanisms of the problem are relatively well understood widely accepted, is generally regarded as "idiopathic" - meaning that it has no known mechanism of causation & it's processes are not fully understood. The problem here is made more difficult still, due to the variable nature of Multiple Chemical Sensitivity from one patient to the next & this often makes treatment with conventional medicine & practices ineffective or inappropriate; for most sufferers with Multiple Chemical Sensitivity, the avoidance of pollutants/toxicants is the key.