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Solar urticaria (SU) is a rare condition in which exposure to ultraviolet or UV radiation, or sometimes even visible light, induces a case of urticaria or hives that can appear in both covered and uncovered areas of the skin.〔 It is classified as a type of physical urticaria. The classification of disease types is somewhat controversial. One classification system distinguished various types of SU based on the wavelength of the radiation that causes the breakout; another classification system is based on the type of allergen that initiates a breakout.〔〔 The agent in the human body responsible for the reaction to radiation, known as the photoallergen, has not yet been identified.〔 The disease itself can be difficult to diagnose properly because it is so similar to other dermatological disorders, such as polymorphic light eruption or PMLE.〔 The most helpful test is a diagnostic phototest, a specialized test which confirms the presence of an abnormal sunburn reaction. Once recognized, treatment of the disease commonly involves the administration of antihistamines, and desensitization treatments such as phototherapy.〔 In more extreme cases, the use of immunosuppressive drugs and even plasmapheresis may be considered.〔 The initial discovery of the disease is credited to P. Merklen in 1904, but it did not have a name until the suggestion of "solar urticaria" was given by Duke in 1923.〔 However, their research contributed to the study of this uncommon disease. More than one hundred cases have been reported in the past century.〔 == Signs and symptoms == Generally, the areas affected are exposed skin not usually protected by clothing; however it can also occur in areas covered by clothing.〔〔 Areas constantly subjected to the sun's rays may only be slightly affected if at all. People with extreme cases will also have reactions to light bulbs that emit a UV wavelength (any bulb that is not an LED). Parts of the body only thinly covered can also potentially be subjected to an outbreak. Life with SU can be difficult. Patients are subject to constant itching and pain, as within minutes of the initial exposure to UV radiation a rash will appear. The urticarial reaction begins in the form of pruritus, later progressing to erythema and edema in the exposed areas of the skin. If vast areas of the body are affected, the loss of fluid into the skin could lead to light-headedness, headache, nausea, and vomiting.〔 Extremely rarely, patients have been reported to experience an increase in heart rate that can cause a stroke or heart attack due to the body cavity swelling. Other rare side effects can be bronchospasm and glucose instability issues. Also, if a large area of the body is suddenly exposed the person may be subject to an anaphylactic reaction. Once free of exposure, the rash will usually fade away within several hours; rare and extreme cases can take a day or two to normalize depending on severity of the reaction. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solar urticaria」の詳細全文を読む スポンサード リンク
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