Solar urticaria is just a fancy way of referring to hives that are induced by exposure to the sun. Although not yet conclusively proven to be at fault, IgE antibodies are believed to be involved in at least some cases. The condition most commonly affects those between the ages of twenty and forty.

Sun-induced hive reactions typically occur within seconds to minutes following exposure and may last for minutes to hours, depending on the intensity of the ultraviolet radiation. Under the microscope and even to the naked eye, the hives produced by ultraviolet light are no different from those that are caused by foods or drugs. Although spontaneous remissions do occur, solar urticaria more frequently persists for life.

Diagnosing solar urticaria is usually a straightforward matter: The patient gives a history of breaking out in hives after being in the sun. To confirm the diagnosis, the dermatologist may perform phototesting. The simplest form of phototesting involves exposing a small area of the patient's skin for the amount of time the person claims causes his reaction. The development of hives following such exposure confirms the diagnosis.

Most people with solar urticaria are extremely sensitive to the sun, making treatment a challenge. Unquestionably, the preventive measures of avoidance of sun exposure and the use of protective clothing whenever outdoors are the best forms of treatment. Sunscreens have proven inadequate for most people with the condition, but the nonsedating antihistamine terfenadine (Seldane) has been shown to be helpful in certain cases.