In the past, some hazardous materials were used in cosmetics such as lead carbonate, bismuth, and mercurials. Serious adverse reactions to cosmetic ingredients and preparations are actually infrequent. However, side effects do occur and are by no means rare. The unwanted effects of cosmetics can be classified in the following categories [1-4]:

1. Irritation and contact urticaria 2. Contact allergy 3. Photosensitive reaction (photoallergy and photoirritation) 4. Acnegenesis and comedogenesis 5. Color changes of the skin and appendages 6. Systemic side effects 7. Other local side effects

When considering skin-irritation symptoms, we are dealing with nonimmunological mediated inflammation of the skin induced by external agents. Chemical irritants are the major cause, but mechanical, thermal, climatic, and UV and IR light are also important factors or cofactors of irritancy [5]. This nonimmunological skin irritancy reaction comprises two forms: the acute irritant reaction with a monofactorial cause (detergent, acid, oxidant, etc.) and the chronic multifactorial form. The symptoms of skin irritation are well known: erythema, dryness, scaling, itching, burning, and tingling. The clinical symptoms are described by some investigators as objective irritation [1-4]. Because these symptoms are clearly perceptible, in vivo testing in humans can easily and reliably detect strong and moderate irritants for cosmetic ingredients and eliminate these potential hazards. However, most cosmetic-use ingredients do not produce acute irritation from a single exposure because they are mild or very mild and consequently difficult to detect. However, they may produce inflammation after repeated application on the same area of the skin, which is referred to as cumulative irritation.