Contact allergy epidemics and their controls

Allergic contact dermatitis--formation, structural requirements, and reactivity of skin sensitizers

Contact allergy is caused by a wide range of chemicals after skin contact. Its clinical manifestation, allergic contact dermatitis (ACD), is developed upon repeated contact with the allergen. This perspective focuses on two areas that have yielded new useful information during the last 20 years: (i) structure-activity relationship (SAR) studies of contact allergy based on the concept of hapten-protein binding and (ii) mechanistic investigations regarding activation of nonsensitizing compounds to contact allergens by air oxidation or skin metabolism. The second area is more thoroughly reviewed since the full picture has previously not been published. Prediction of the sensitizing capacity of a chemical is important to avoid outbreaks of ACD in the population. Much research has been devoted to the development of in vitro and in silico predictive testing methods. Today, no method exists that is sensitive enough to detect weak allergens and that is robust enough to be used for routine screening. To cause sensitization, a chemical must bind to macromolecules (proteins) in the skin. Expert systems containing information about the relationship between the chemical structure and the ability of chemicals to haptenate proteins are available. However, few designed SAR studies based on mechanistic investigations of prohaptens have been published. Many compounds are not allergenic themselves but are activated in the skin (e.g., metabolically) or before skin contact (e.g., via air oxidation) to form skin sensitizers. Thus, more basic research is needed on the chemical reactions involved in the antigen formation and the immunological mechanisms. The clinical importance of air oxidation to activate nonallergenic compounds has been demonstrated. Oxidized fragrance terpenes, in contrast to the pure terpenes, gave positive patch test reactions in consecutive dermatitis patients as frequently as the most common standard allergens. This shows the importance of using compounds to which people are exposed when screening for ACD in dermatology clinics.

Contact dermatitis: epidemiology and frequent sensitizers to cosmetics

Contact dermatitis is defined as a pattern of inflammatory response that may occur as a result of contact with external factors. The two most common causes are irritants and allergens. Very few reliable data on prevalence and incidence of contact dermatitis exist, and data from the few studies that have been carried out cannot be compared because of differences in methodology. Occupational contact dermatitis constitutes up to 30% of all occupational diseases for which compensation is payable and affects sufferers' home and social lives as well as their working lives. Patients can be advised about the use of personal protective equipment and creams and emollients to avoid or ameliorate their condition, but there is little epidemiological evidence for their efficacy. Patch testing, using the European Standard Series of Allergens, is necessary to determine which agent is responsible for the condition. Fragrances and preservatives used in cosmetics are among the most common allergens in contact allergic dermatitis, although the frequency of contact allergy in the general population is small. It is to be hoped that the European Dermato-Epidemiology Network Fragrance Study will go some way to addressing the need for a large population-based epidemiological study in order that public health organizations can give reliable advice about avoiding and treating contact dermatitis.