Allergies and Chemical Sensitivities:

"A trend noted by many people has been an increase in what seems to be allergic reactions in the general population. Ranging from congestion to sneezing to more severe reactions such as rashes, breathing problems and worse, these reactions are often non-specific to natural allergens. Some activists and researchers have identified chemicals as potential factors in these reactions. Multiple Chemical Sensitivity (MCS) is the name given to the broad issue of reactions to specific or cumulative chemicals in the environment."

See the Facts on MCS by Ohio State University:
http://ohioline.osu.edu/cd-fact/0192.html

Also see:
http://www.multiplechemicalsensitivity.org/

and by the American Academy of Family Physicians:
http://www.aafp.org/afp/980901ap/magill.html