The ingredients responsible for allergy to cosmetics were determined in 119 patients suffering from cosmetic-related contact dermatitis. Most reactions (56.3%) were caused by skin care products, followed by nail cosmetics (13.4%), perfumes (8.4%), and hair cosmetics (5.9%). Preservatives were most frequently implicated (32.0%), followed by fragrances (26.5%) and emulsifiers (14.3%). By far the most important cosmetic allergen was Kathon CG, (a preservative system containing, as active ingredients, a mixture of methylisothiazolinone and methyl chloroisothiazolinone) reacting in 33 patients (27.7%). Other frequent causes of cosmetic-related contact allergic reactions were toluenesulfonamide/formaldehyde resin in nail hardener and/or nail lacquer (15 patients [12.6%]), and oleamidopropyl dimethylamine, an emulsifier in baby body lotion (13 patients [10.9%]).