Your doctor can most likely make a diagnosis of polymorphous light eruption based on your answer to questions and a physical exam. Laboratory tests may be needed to confirm a diagnosis or rule out other conditions.
Your doctor will conduct an exam to assess your general health. In particular, he or she will examine the rash and the condition of your skin at other sites.
Your doctor may order one of the following tests if a diagnosis isn't certain, the rash doesn't resolve at an expected rate, or there is any reason to suspect another condition causing the rash. Tests may include:
- Skin biopsy. Your doctor may scrape a tiny portion of the rash to remove a sample of tissue (biopsy) for examination in a lab. The biopsy is primarily used to rule out other conditions that may be causing a rash.
- Blood tests. A nurse or assistant may draw blood for laboratory tests that can rule out other conditions.
- Phototesting. You may be referred to a dermatologist for phototesting. During the test small areas of your skin are exposed to measured amounts of UVA and UVB light to try to reproduce the problem. If your skin reacts to the UV radiation, you're considered sensitive to sunlight (photosensitive) and may have polymorphous light eruption or another light-induced disorder.
Other light-induced conditions
Your doctor may need to rule out other disorders characterized by light-induced skin reactions. These conditions include:
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- Chemical photosensitivity. A number of chemicals — drugs, medicated lotions, fragrances, plant products — can induce photosensitivity. When this occurs, your skin reacts each time it's exposed to sunlight after ingesting or coming into contact with a particular chemical.
- Solar urticaria. Solar urticaria is a sun-induced allergic reaction that produces hives — raised, red, itchy welts of various sizes that appear and disappear on your skin. The welts can appear within a few minutes of sun exposure and last for a few minutes to hours. Solar urticaria is a chronic condition that can last for years.
- Lupus rash. Lupus is an inflammatory disorder that affects a number of body systems. One symptom is the appearance of a discolored, bumpy rash on areas of skin exposed to sunlight, such as the face, neck or upper chest.
- Habif T. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 5th ed. Philadelphia, Pa.: Mosby Elsevier; 2009. http://www.mdconsult.com/books/page.do?eid=4-u1.0-B978-0-7234-3541-9..00028-6--s0355&isbn=978-0-7234-3541-9&type=bookPage§ionEid=4-u1.0-B978-0-7234-3541-9..00028-6--s0355&uniqId=227127777-3#4-u1.0-B978-0-7234-3541-9..00028-6--s0355. Accessed Nov. 18, 2010.
- Honigsmann H. Polymorphous light eruption. Photodermatology, photoimmunology & photomedicine 2008;24:155.
- Facts about sunscreens. American Academy of Dermatology. http://www.aad.org/media/background/factsheets/fact_sunscreen.htm. Accessed Nov. 18, 2010.
- Bylaite M, et al. Photodermatoses: Classification, evaluation and management. The British Journal of Dermatology 2009;161(suppl 3):61.
- Systemic lupus erythematosus (SLE). The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/sec04/ch032/ch032g.html. Accessed Nov. 19, 2010.
- Photosensitivity. The Merck Manuals: The Merck Manual for Healthcare Professionals. http://www.merckmanuals.com/professional/sec10/ch115/ch115c.html. Accessed Nov. 19, 2010.
- Sun-protective clothing: Wear it well. Federal Trade Commission. http://www.ftc.gov/bcp/edu/pubs/consumer/alerts/alt094.shtm. Accessed Nov. 18, 2010.