Many of these types of urticaria can occur together in a person with CU.
Aquagenic urticaria occurs on contact with water. This is a very rare form of urticaria, and is different from cold urticaria and cholinergic urticaria in that the temperature of the water does not matter. It is diagnosed by applying tepid water to the patient’s skin.
Cholinergic urticaria results from a rise in core body temperature. It occurs with exercise, sweating, and passive warming, as well as elevated air temperatures. The rash of cholinergic urticaria is smaller than classic urticaria, and itching may occur without the presence of wheals. It is typically diagnosed by inducing sweating, either with exercise or immersing the hand in hot water.
Cold-induced urticaria occurs after exposure of the skin to cold temperatures, particularly in damp and windy weather. Diagnosis is generally made by rubbing an ice cube on the patient’s forearm or immersing the hand in cold water to see if wheals appear.
Dermographism (also called dermatographism) is a wheal-and-flare response to rubbing or firm stroking of the skin. The stimulus can be a hard shower, clapping of the hands, or scratching, to name a few. Dermographism is often diagnosed by simply scratching on the patient’s skin and observing the response.
Delayed pressure urticaria (DPU) occurs as a delayed response to pressure against the skin. Hives may not appear for as much as six hours after the pressure stimulus. The pressure can be from clothing, walking, leaning against something, etc. DPU can be distinguished from dermographism by the fact that hives arise much later and last longer than with dermographism. Diagnosis is made by applying pressure to the patient’s skin and observing the area six hours later.
Solar urticaria comes from exposure to the sun, and only the parts of the skin exposed to the sun are affected. This is a rare form of urticaria. It is diagnosed by exposing the patient’s skin to the sun.
Scott, C.B. and Moloney, M.F. (1996). Physical urticaria: A common misdiagnosis. The Nurse Practitioner, 21(11), 42-59.
Wanderer, Alan. (2003). Hives: The Road To Diagnosis and Treatment of Urticaria. Bozeman, MT: Anson Publishing