Since most information on adverse reactions to cosmetics is obtained from consumer complaints to the cosmetic manufacturer or to the FDA, the precise incidence of these problems is not really known. Many consumers who have a problem with one product or another simply switch brands in a trial-and-error fashion without letting anyone know.

Considering the enormous number of people using so many different kinds of cosmetics during their lifetimes (millions of people use them every day), the actual total number of adverse reactions to cosmetics is believed to be surprisingly small. Of these, irritant rather than true allergic contact allergies make up the greatest proportion, more than 90 percent. This means that only about one in every ten reactions to cosmetics is a true allergic reaction. Occasionally, however, these reactions may be quite troublesome or severe, requiring medical attention.