Contact urticaria--a review.

Contact urticaria is a wheel and flare reaction occurring within 30 to 60 minutes after skin and mucosal contact. The pathogenesis of contact urticaria include an immunologic mechanism, a non-immunologic mechanism and an uncertain mechanism. Important immunologic contact urticants are animal products, foodstuffs and rubber latex. Important non-immunologic contact urticants are preservatives and flavouring agents in cosmetics and foods. Ammonium persulphate produces contact urticaria where the mechanism is uncertain. The prick test is a useful diagnostic test for contact urticaria but must be done with caution, especially in persons who has a history of anaphylactoid reaction. The guinea pig ear is a model for testing non-immunologic contact urticants.