It seems like anything can cause hives, even the sun! Solar urticaria.

Did you know that the sun can trigger an outbreak of hives? Although rare, this is indeed true!

This is known as Solar Urticaria.

This is a type of “physical” urticaria or hives triggered by exposure to visible and ultra-violet light (UV radiation). It was first described in 1904 with more than 100 cases described in the last century. The hives can be provoked by exposure to natural sunlight or artificial light sources (tanning beds, bluish dentist lights and lights used by beauticians when applying artificial fingernails). The wavelengths of light that are most often implicated range from 280-760 nanometers (nm) which is typically green or blue. The ultraviolet lights are subdivided into UV-A nm – 320 nm, UV-B 320 nm – 290 nm and UV-C 290 nm – 100 nm. Visible light is 400-800 nm.

Hives (itching, burning, red, slightly raised welts) occur on the exposed areas and even through light clothing. The hives disappear within several minutes to a few hours leaving the skin appearing normal if there is no continued sun exposure.

Solar Urticaria: Who does it affect?

• All races and throughout the world.

• Estimated to occur in 5 out of 1,000 patients with chronic hives. Rare!

• Women are more affected in most studies.

• Average age of onset is 35 years old, but symptoms can begin from 17-71 years old. It is very rare in infancy.

• It does not appear to be hereditary.

What causes Solar Urticaria?

• The mast cells (allergy/immune cells) in the skin will release histamine leading to the formation of hives when proteins in the skin are changed upon exposed to the wavelengths of light. The exact mechanisms are unknown.

Is Solar urticaria dangerous?

If a large area of the body is exposed to light, the resulting release of histamine and other chemical mediators can lead to more generalized symptoms such as anaphylaxis.

Diagnosis of Solar Urticaria:

• The pattern of hives occurring after sunlight or other UV exposure is suggestive. However, there are other disorders where skin rash occurs with sun exposure that should be evaluated including polymorphous light eruption, porphyria (metabolic disorder) and drug-induced photo-allergic reactions.

• Photo-test: your dermatologist will have a device that emits different wavelengths of light and confirm the MUD (minimum urticarial dose). A visible light source such as an old fashioned slide projector can be used although a water filter should be placed in front to decrease the amount of heat generated (the heat could trigger cholinergic or heat induced hives). It may take up to an hour of visible light to trigger the hives. Other more sophisticated light emitting devices such as laser or solar simulators may be necessary. If conditions are right, testing with direct sunlight can be performed.

There is no cure and it rarely goes away on its own, but…

Treatment of Solar Urticaria:

• Stay out of the sun! (especially between 11 am and 3 pm)

• Wear protective clothing

• Place UV shades over windows

• Learn how much sunlight your skin can tolerate and keep exposure below that threshold

• Use Sunscreen SPF 30 (UVB protection) and remember to re-apply often

• Oral antihistamines may prevent hives to some degree, allowing some tolerance to sunlight. The best choice would be long-acting new generation formulations such as loratadine, fexofenadine, or cetirizine.

• Phototherapy (also known as desensitization or UV treatment may be performed by your dermatologist). Exposure of your skin to UV-A or broadband or narrowband UV-B light several times a week over a period of 5 weeks may help.

• Photo-chemotherapy where oral methoxsalen is added to UV-A may provide longer-lasting improvement.

• Vitamin D supplementation: Vitamin D is made in the skin and requires a certain amount of sun exposure. Since this isn’t recommended, taking Vitamin D may be necessary. A blood test for Vitamin D levels can help guide your doctor.

• In the spring, gradually exposing your skin to a slightly longer duration of sun exposure may help for mild cases.

• For extreme cases, IVIG, plasmapheresis, and immuno-suppressive medications have been used.

At Family Allergy Asthma & Sinus Care, we frequently see patients with hives. It is truly a puzzle when it comes to the diagnosis. It’s a good thing we like solving puzzles…