Solar urticaria | |
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Formation of wheals on the arm | |
Specialty | Dermatology |
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.[1][2] It is classified as a type of physical urticaria.[3] 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.[4][5]
The agent in the human body responsible for the reaction to radiation, known as the photoallergen, has not yet been identified.[6] The disease itself can be difficult to diagnose properly because it is so similar to other dermatological disorders, such as polymorphous light eruption or PLE.[7] 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.[1] In more extreme cases, the use of immunosuppressive drugs and even plasmapheresis may be considered.[8]
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 William Waddell Duke in 1923.[9][10] However, their research contributed to the study of this uncommon disease. More than one hundred cases have been reported in the past century.[11]
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