Chronic urticaria.

Urticaria affects 15% to 20% of the population once or more during a lifetime. Chronic urticaria is a frequent recurrent eruption over a period greater than 6 weeks; the cause remains a mystery in more than 75% of cases. Urticaria and angioedema may be produced by immunologic or nonimmunologic means. Urticarial vasculitis, contact urticaria, mastocytosis, physical urticarias, dermatographism, cholinergic urticaria, localized heat urticaria, cold urticaria, aquagenic urticaria, and vibratory angioedema all require specific evaluation and treatment. Chronic idiopathic urticaria is usually controlled by antihistamines; depending on the circadian rhythm of the eruption, sedative or nonsedative antihistamines are prescribed. Some patients will require a combination of H1 and H2 antagonists, or even parenteral corticosteroids.