Overview of Solar Urticaria

An itchy rash that develops within minutes of sun exposure

Sun Rash
Sun exposure can cause allergic rashes. Tom and Steve Collection/Getty Image

Some people rarely develop a form of chronic hives called solar urticaria within minutes of being out in the sun. The itchy, red bumps or wheals of this rash only develop on areas of the body directly exposed to the sunlight.

At times, symptoms of solar urticaria can be confused with a sunburn, although solar urticaria usually occurs within five to ten minutes of exposure to the sun, and goes away much quicker (less than a day) after the sun exposure has stopped.

You may be surprised to learn that in solar urticaria, the skin that is frequently exposed to sunlight, such as the skin on the face or the tops of the hands, is unlikely to develop hives, as opposed to skin that is less frequently exposed to the sun. Also, while the rash of solar urticaria technically only occurs on skin that is directly exposed to the sun, it may occur under thin clothing.

Cause of Solar Urticaria

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.

Diagnosis of Solar Urticaria

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.

Treatment of Solar Urticaria

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.

In more severe cases, a medication like omalizumab (an antibody against immunoglobulin E) has been tried with mixed results. More research needs to be done on omalizumab and its potential benefit in alleviating solar urticaria. That being said, solar urticaria is an uncommon condition, so it's difficult to study scientifically.

A Word From Verywell

While solar urticaria is a chronic form of hives and can be quite disabling for some, the good news is that there are effective therapies out there and one or more medications in the pipeline.

In addition to solar urticaria, there are also other forms of heat-related rashes like cholinergic urticaria, a form of hives worsened by heat.

Sources:

Aubin F et al. Omalizumab in patients with severe and refractory solar urticaria: A phase II multicentric study. J Am Acad Dermatol. 2016 Mar;74(3):574-5.

Goetze S, Elsner P. Solar urticaria.J Dtsch Dermatol Ges. 2015 Dec;13(12):1250-3.

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