Diagnosing and treating chronic urticaria.

Chronic urticaria is differentiated from the acute type by its persistence and by its causative agents. It can result from histamine, and other chemical mediators, released from damaged mast cells either by an antigen-antibody reaction or some other mechanism. The cause, often elusive, may be common foods or medications. External temperature changes can be manifested by urticaria through various mechanisms. The endogenous causes include chronic foci of infections such as in teeth, sinuses or tonsils, endocrine changes, parasitic infestations. Chronic urticaria may be a symptom of underlying more serious systemic diseases such as lymphomas.