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Solar urticaria is a rare type of skin hives. With this condition, the skin will well up into hives within just minutes of being exposed to artificial sunlight, natural sunlight, or anything emitting ultraviolet radiation.
This condition can be very disabling and the reaction can last from just a few minutes to more than an hour. An antigen-antibody reaction is thought to cause this condition, but exactly how is happens is unknown. It seems that photoallergen, a chemical created in the body, will react with UV radiation and then cause an allergic reaction in the form of urticaria.
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Signs and Symptoms
Within less than 30 minutes of being exposed to sun, an itchy, stinging rash develops. The rash may be swollen and red and appear like weals. The rash typically affects the areas of the skin that are typically not exposed to sunlight, such as the back. The areas that are often exposed to sunlight, such as the upper area of the hands and the face, are normally either not at all affected or just slightly affected. If a lot of the body is affected, significant fluid loss is possible, which may result in nausea and vomiting, headache, and lightheadedness.
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This condition cannot be diagnosed based only on the patient's symptoms. Other conditions may have similar signs and symptoms, such as certain types of porphyria and polymorphous light eruption, so testing is needed to make an accurate diagnosis. Doctors will expose the patient's skin to a variety of different light forms that can produce a variety of wavelengths, or spectrums. This test is specialized and performed by a dermatologist in most cases. In some cases, exposure to natural sunlight can make a diagnosis.
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Antihistamines are generally effective in reducing the symptoms of solar urticaria. Most patients benefit from over-the-counter forms, but some patients may need a prescription antihistamine. Hydrocortisone, and other topical steroids, are also often helpful in reducing symptoms. When symptoms are severe, prednisone, and other oral steroids, may be necessary to reduce symptoms.
In some cases, the skin can be desensitized by having the patient repeatedly expose his or her skin to sunlight to help the hives no longer occur when the patient is exposed to sunlight in the future. This type of therapy is specialized and patients should never try it on their own. Those who wish to try this therapy must due to so under the direct supervision of a dermatologist or an allergist. The treatments are frequent and are only usually done for a few days.
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New Zealand Dermatological Society. (2006). Solar Urticaria. Retrieved on January 30, 2011 from the New Zealand Dermatological Society: http://www.dermnetnz.org/reactions/solar-urticaria.html
Ferguson, J. (2005). Solar Urticaria. Retrieved on January 30, 2011 from NetDoctor: http://www.netdoctor.co.uk/diseases/facts/solarurticaria.htm