A preservative system for cosmetics and toiletries containing as active ingredients a mixture of methylisothiazolinone and methylchloroisothiazolinone (1.5%) is an important cause of cosmetic allergy in many European countries. Most cases have been caused by products of the "leave-on" variety, such as moisturising creams. The use of isothiazolinone preservative in such products should be abandoned. More critical evaluation of its sensitising potential before marketing might have prevented the continuing epidemic of allergic cosmetic dermatitis due to this preservative. New chemicals should undergo extensive toxicological evaluation before their use in cosmetics is allowed. Ingredient labelling should be made a legal requirement.