New aspects in allergic contact dermatitis.

To give selected new information on contact allergy and allergic contact dermatitis with focus on diagnostic procedures and pitfalls. Recent studies dealing with common contact allergens have improved our understanding of the relationship between positive patch tests and the clinical interpretation and consequences for the patient. Nickel allergy is still the most common contact allergy in Europe in spite of full implementation of the EU Nickel Directive in 2001. Contact allergens in cosmetics and topical drugs are another common cause of allergic contact dermatitis. The main culprits include fragrance chemicals, preservatives, and hair dyes. We are all more or less exposed to cosmetics and topical drugs on a daily basis. The labelling requirements given in the Cosmetics Directive is of great help in tracing the causative allergenic ingredients. Most of the components present in cosmetic products are also occurring in household and industrial products, often under other trade names. Patients with multiple contact allergies constitute a special problem because their quality of life is severely affected by the multitude of eliciting products in the environment. We still lack a good understanding of why these patients become so easily sensitized.