During 64 months (1977 to 1983), twelve dermatologists from various sections of the United States studied a total of 713 patients with cosmetic dermatitis out of an estimated total of 13,216 patients with contact dermatitis. The number of patients seen for all causes during this period was 281,100. An important finding was that half of the patients or physicians were unaware that a cosmetic was responsible for their dermatitis. Skin care products, hair preparations (including colors), and facial makeup were responsible for the majority of the reactions. The most important objective was identification of causative ingredients. Eighty-seven percent of the subjects had patch tests. Fragrance, preservatives (Quaternium-15, formaldehyde, imidazolidinyl urea, and parabens), p-phenylenediamine, and glyceryl monothioglycolate were the most frequently identified allergic sensitizers, in that order. In addition to the clinical data, the study permitted assessment of the frequency of cosmetic reactions, although the data may not be entirely representative of the country at large because of the special interests of the dermatologists involved.