Physical urticaria is a condition in which red (erythematous) allergic skin lesions and itching (pruritus) are produced by exposure to heat, cold, or contact with chemicals or plants. These are called wheals by the medical community and may range in size from a couple of millimeters to a couple of centimeters. The center of the lesion may range in color from white to red, and it is usually surrounded by a flare of red skin. The disorder occurs most commonly in children.
The most common symptoms of physical urticaria are itching (pruritus) and hives consisting of red rings around white ridges (wheals). Sensitivity to cold is usually manifested by these eruptions on the skin, itching, and swelling under the skin (angioedema). These symptoms develop most typically after exposure to cold is terminated and during or after swimming or bathing. Contraction of the muscles around the bronchi (bronchospasm) and even histamine-mediated shock may occur in extreme cases. If this happens during swimming, drowning may present a danger.
Sensitivity to cold can be passively transferred with serum that contains a specific immunoglobulin (IgE) antibody, suggesting an allergic reaction involving a physically altered skin protein as the cause of the allergic reaction. The serum of a few patients with cold-induced symptoms of physical urticaria contains cryoglobulins or cryofibrinogen, these abnormal proteins can also be associated with a serious underlying disorder such as a malignancy, a collagen vascular disease, or chronic infection. Cold may aggravate asthma or vasomotor rhinitis, but cold urticaria is independent of any other known allergic tendencies.
Dermatographia, dermographism, or autographism describes welts or wheels produced by scratching or firmly stroking the skin. According to some dermatologists, dermographism is the most common form of physical urticaria. This sign can appear quite suddenly and may become apparent in hot weather or after a hot shower or bath. Occasionally it is the first sign of an urticarial drug reaction. Physical urticaria has also occurred following persistent vibration of the skin, and even after exposure to water (aquagenic urticaria).
The underlying cause of physical urticaria is unknown in most cases. Some clinicians believe that an auto-immunological process is responsible.
Cold urticaria occurs most often in infants, although it sometimes occurs in adults.
The patient history and physical examination are the tools most often used to diagnose physical urticaria. If there is a history of reactions to physical triggers, the diagnosis may be confirmed with a challenge. The challenge is the application of the suspected agent, for example ice or light, to the skin, in hope of getting a response.
Protection from and avoidance of the physical cause of the reaction is necessary. Symptoms such as itching and swelling can usually be relieved with an oral antihistamine. The more powerful systematic (intravenous) corticosteroids should be avoided unless they are vital.
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Strachan DD. Urticaria, Chronic. Last Updated: March 31, 2005. 15pp.