Sun hives are generally caused by an allergy to sunlight. While many skin conditions can cause sun allergies, solar urticaria is the condition most likely to cause sun hives. Inflammation and itching typically accompany the hives, which usually appear with sun exposure.
Urticaria is a skin condition that commonly causes hives, usually when the person comes into contact with a physical trigger. These triggers can include temperature changes, atmospheric pressure changes, water, and physical activity. For some people, exposure to sunlight triggers the symptoms of urticaria. This type of urticaria is commonly known as solar urticaria.
Solar urticaria is considered a chronic condition. It generally causes inflammation, itching, blisters, and hives on skin exposed to natural sunlight. The sun hives typically appear only on parts of the body exposed to sunlight. They can appear almost immediately, and usually go away again within a few hours if sun exposure is eliminated.
Physicians believe that an autoimmune response is responsible for the skin condition known as solar urticaria. People with this condition may form antibodies against naturally occurring proteins in their own skin. Sun exposure typically changes the chemical composition of these naturally occurring proteins, which can trigger an immune response against them. This immune response is considered responsible for the inflammation, itching, blisters, and sun hives associated with solar urticaria. If a person suffering from solar urticaria exposes too much of their skin to the sunlight, anaphylaxis can occur.
Solar urticaria is typically diagnosed by exposing the skin to different wavelengths of UV light. Dermatologists are considered most able to accurately diagnose this condition. Some patients may need to expose skin to natural sunlight, rather than the light produced by specialized UV lamps, in order to obtain an accurate diagnosis.
Antihistamine or steroid medications are generally used to treat the allergic reaction to sunlight associated with solar urticaria. Topical creams are generally prescribed to treat mild to moderate sun hives. Oral medications may be necessary to treat those who suffer from severe reactions to sunlight.
Ultraviolet light therapy can help improve symptoms for some patients. This therapy involves using UV lamps to gradually desensitize some areas of the body to natural sunlight. These lamps are most often used on the face, hands, and other areas likely to experience the most sun exposure. Ultraviolet light therapy can take several weeks, but many patients find that it significantly increases the skin's ability to tolerate exposure to natural sunlight.