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Causes
By Mayo Clinic staffAllergic reactions to sunlight occur when ultraviolet radiation triggers changes in your skin cells. These changes cause your immune system to mistakenly identify proteins in your skin cells as harmful invaders. Your immune system then releases antibodies that attack the cells, and this leads to symptoms.
For most people with a sun allergy, exposing bare skin to bright sunlight during the spring or summer triggers the allergic skin reaction. However, some people can have a reaction during winter months. In people who have a severe sun allergy, an allergic reaction may even be triggered by indoor lights.
Certain medications, chemicals and medical conditions can make the skin more sensitive to the sun (photosensitivity). For example, an ingredient in your shampoo or having a condition such as lupus can increase photosensitivity. In most cases this isn't a true allergic reaction. However, it can cause symptoms similar to those caused by a sun allergy — and if you already have a sun allergy, it can make your symptoms worse.
It isn't clear why some people have a sun allergy, and others don't. Inherited traits may play a role.
- 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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