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Sun Rash


Updated May 31, 2014

Sun Rash
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What is a Physical Urticaria?

People who have a physical urticaria have a physical trigger for their hives, such as pressure, heat, cold, sunlight, water, or exercise. Up to 20 to 30% of people with chronic urticaria have a physical cause.

What is Solar Urticaria?

Solar urticaria is a form of chronic hives that is caused by exposure to sunlight. People with this condition experience itching, redness and hives on areas of skin exposed to sunlight. At times, symptoms can be confused with a sunburn, although solar urticaria can occur within minutes of exposure to the sun, and goes away much quicker (less than a day) after sun exposure has stopped.

The appearance of the hives is no different from other forms of urticaria, although these hives only occur on skin that is directly exposed to the sun. Hives may also occur under thin clothing. Skin that is frequently exposed to sunlight, such as the skin on the face, is typically unlikely to develop hives as opposed to skin that is less frequently exposed to the sun.

It appears that people with solar urticaria make allergic antibodies against various proteins found in their own skin. These proteins' structure changes with sunlight, allowing the allergic reaction to occur, causing hives. It is possible for a person with solar urticaria to experience anaphylaxis if enough skin is exposed to sunlight.

How is Solar Urticaria Diagnosed?

A solar urticaria diagnosis cannot be made by a person’s history of symptoms alone, since other conditions, such as polymorphous light eruption and certain forms of porphyria, can also cause skin rashes with sun exposure. A diagnosis is made when the skin is exposed to various forms of light that can produce different spectrums, or wavelengths. This is a specialized test that is most often performed by dermatologists, who have the specialized equipment available for such testing. Sometimes a diagnosis can only be made with exposure to natural sunlight.

How is Solar Urticaria Treated?

Symptoms can be decreased with the use of various antihistamines, as well as the application of topical steroid creams, such as hydrocortisone. Occasionally, oral steroids, such as prednisone, are required to treat severe symptoms.

It is possible to desensitize the skin with repeated exposure to sunlight so that hives will not occur with future exposures. This specialized form of therapy, which should only be performed by an allergist or dermatologist, typically only lasts for a few days, and therefore needs to be repeated frequently.

Want to keep learning? Find out about cholinergic urticaria, a form of hives worsened by heat.


Dice, JP. Physical Urticaria. Immunol Allergy Clin N Am. 2004;24:225-246.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.

  1. About.com
  2. Health
  3. Allergies
  4. Skin Allergies
  5. Urticaria (Hives)
  6. Sun Rash or Solar Urticaria Diagnosis and Treatment

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