The contact urticaria syndrome.

Contact urticaria may occur following contact of the skin or mucous membranes with a large number of diverse substances. When localized angioedematous reactions of the eyes or oropharynx are caused by proteinaceous substances, the distinction between contact urticaria and common inhalant or food allergies is subtle. The time course of the reaction, negative controls, or occurrence of generalized symptoms do not constitute unequivocal evidence of immunologic contact urticaria, and confirmation by RAST or passive transfer testing is required. Clinical symptoms range from mild, localized erythema to generalized anaphylaxis. When contact urticaria becomes superimposed on eczematous skin, immediate reactions that resemble eczema more than urticaria may occur. Dermatologists must increase their awareness of these clinical reactions and evaluate the external environment when searching for causes of localized urticarial reactions.