What is it?

Solar urticaria is a rare form of chronic inducible urticaria (hives) in which the skin swells within minutes of exposure to natural sunlight or an artificial light source emitting ultraviolet radiation. The reaction may subside within a few minutes or it may persist for up to an hour or more where it can become very disabling.

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Signs & symptoms

A stinging, itchy rash develops within minutes after a short period (less than 30 minutes) of sun exposure. The rash may look like weals and be red and swollen. Often the rash affects areas of exposed skin that are normally shielded from sunlight by clothing, e.g. back. The face and upper sides of the hands that are constantly exposed to the sun may be unaffected or only slightly affected. This may be put down to acclimatisation or 'hardening' of these chronically exposed areas.
If large areas of the body are affected, the loss of fluid into the skin may result in light-headedness, headache, nausea and vomiting.
Areas covered with thin clothing may also be affected, depending on the ultraviolet rays being emitted and the sheerness of the fabric.

Diagnosis

The clinical features of solar urticaria may appear similar to other photodermatoses so it is important to take an accurate history from patients. Defining features of solar urticaria include:
* Rash appearing within a few minutes of exposure. In rare cases, some solar urticaria patients may show a delayed reaction to sunlight.
* Upon cessation of sun exposure the rash quickly disappears (within minutes to a few hours, rarely lasting more than 24 hours).
Phototesting is used to confirm the diagnosis.

Treatment

As soon as a patient is shielded from sun exposure the rash begins to disappear spontaneously within several minutes to a few hours. The rash clears away completely without leaving a mark.
Patients with solar urticaria must take measures to avoid or minimise sun exposure by following sun protection strategies. Oral antihistamines may be helpful in reducing weals and minimising pruritus but they rarely prevent the reaction altogether.
For patients that react severely and are unable to manage their condition through preventative measures, phototherapy and/or photochemotherapy may be considered. These treatments desensitise the patient to UV radiation and are often performed prior to the summer months. Desensitisation is often short-lived and repeated therapy may be needed.

☝️ This is not a substitute for professional medical advice. Please consult with your physician before making any medical decision.

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