Physical urticaria.

Physical urticarias are a unique subgroup of chronic urticaria in which patients develop urticaria secondary to environmental stimuli. Common triggers include exercise, temperature changes, cold, heat, pressure, sunlight, vibration, and water. Systemic symptoms have occurred during severe episodes. Physical urticarias are responsible for approximately 20% to 30% of all cases of chronic urticaria. A basic knowledge of these unusual disorders is important for all healthcare providers. This article covers the following types of physical urticarias: dermatographism, cholinergic urticaria, local heat urticaria, exercise-induced anaphylaxis, vibratory angioedema, solar urticaria, and aquagenic urticaria.