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Tests and diagnosis
By Mayo Clinic staffYour doctor will want to make sure your skin reaction isn't due to something other than a sun allergy. A number of conditions can cause similar symptoms. In some cases, a skin allergy can be diagnosed by answering questions or by having your doctor examine the affected areas when symptoms are present. However, if the diagnosis isn't clear-cut, you may need tests to help identify what's going on. If this is the case, you'll most likely need to see a dermatologist.
Tests to diagnose skin reactions caused by sun exposure can include:
- UV light testing. Also called phototesting, this exam is used to see how your skin reacts to different wavelengths of ultraviolet light from a special type of lamp. Determining which particular kind of UV light causes a reaction can help pinpoint which sun allergy you have.
- Photopatch testing. This type of test is used if your doctor suspects something you've come in contact with makes your skin react to sunlight. To do the test, your doctor will apply two identical patches of a substance that may be causing a reaction to your skin. After 24 hours, your doctor will expose one area to UV light, but not the other. If a reaction occurs only on the exposed area, it's likely your reaction is linked to the substance in question. Light testing and photopatch testing are generally available only at specialized clinics.
- Blood tests and skin samples. These tests usually aren't needed. However, your doctor may order one of these tests if he or she suspects your symptoms might be caused by an underlying condition such as lupus instead of a sun allergy. With these tests, a blood sample or a skin sample (biopsy) is taken for further examination in a laboratory.
- Gambichler T, et al. American Journal of Clinical Dermatology. Immunologically mediated photodermatoses diagnosis and treatment. 2009;10:169.
- Millard T, et al. Photosensitivity disorders cause, effect and management. American Journal of Clinical Dermatology. 2002;3:239.
- Ofori AO, et al. Overview of cutaneous photosensitivity: Photobiology, patient evaluation, and photoprotection. http://www.uptodate.com/home/index.html. Accessed March 23, 2010.
- Ferguson J. Diagnosis and treatment of the common idiopathic photodermatoses. Australasian Journal of Dermatology. 2003;44:90.
- Ofori AO, et al. Photosensitive disorders (photodermatoses): Clinical manifestations, diagnosis, and treatment. http://www.uptodate.com/home/index.html. Accessed March 23, 2010.
- Lenane P, et al. Sunscreens and the photodermatoses. Journal of Dermatological Treatment. 2001;12:53.
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