Heat urticaria is an extremely rare condition in which hives develop 2 to 5 minutes after contact with a warm stimulus. The hives usually resolve within 1 hour. This condition is also called localized heat urticaria distinguishing it from generalized heat urticaria, or cholinergic urticaria.
Heat urticaria is diagnosed by apply a test tube of warm water to the skin of the forearm. The characteristic hives should develop within minutes.
Antihistamines may be helpful to treat heat urticaria. Some patients have been treated with desensitization with hot baths, but this therapy must be initiated under medical care.