Solar urticaria

When exposed to light, the skin cells of someone with solar urticaria release potent chemicals (including histamine), causing their blood vessels to open and fluid to collect within the skin. Their skin feels itchy and has red patches, which may be swollen. These may look like weals or a nettle rash, and can take up to an hour to appear after exposure to light, then coming on quickly and settling within a similar period. There is no permanent change to the skin.

Is solar urticaria serious?

If a large enough area of the body is affected, the loss of fluid into the skin may result in light-headedness, pallor and nausea. It's important if you have this complaint to avoid developing a state of shock by limiting the affected areas.

Who suffers from solar urticaria?

Solar urticaria can affect both sexes and may occur at any time of life.

Why does it happen?

Although this is not clearly understood, it seems that a chemical is created in the body that reacts to light, producing an allergic reaction which shows as urticaria. The initial trigger for this condition is unknown.

Is a cause ever found?

Solar urticaria sometimes develops in patients who are taking a drug (aspirin and morphine-like medicines) or are exposed to a particular chemical. By avoiding contact with these agents, the condition may resolve.

How do you know if you have solar urticaria?

Usually, a doctor diagnoses the condition, often using phototesting (where an instrument studies the effects of light on the skin) and blood tests to confirm the diagnosis.

Different doses of ultraviolet and visible wavelengths are shone (usually on the skin of the back) to measure a person's sensitivity to each part of the light spectrum, with the response compared to that seen in normal subjects.

Is there anything that can be done to prevent and treat the eruption?

- Avoid sunlight when possible, particularly between the hours of 11am and 3pm.
- Use 'protective' clothing, such as a wide-brimmed hat, long-sleeved cotton top, and trousers.
- Apply high-protection, broad-spectrum sun barriers frequently.
- Antihistamine tablets can help to abolish or partially induce a remission of the condition in 60 per cent of subjects.
- Phototherapy or desensitisation phototherapy can be used to artificially toughen the skin of those affected by the condition. Patients are usually treated three to five times per week, receiving a total of 15 exposures. The result is skin thickening and pigmentation, which can improve a patient's tolerance to light.
- Occasionally, specialised forms of treatment are needed.

Plasmapheresis - a technique in which some of the patient's blood plasma is removed by machine and the red blood cells are then returned to the patient's circulation. This removes a circulating factor from the blood that may be involved in causing the urticaria, and is demonstrably present in a small proportion of patients. The technique is still being evaluated and is not always effective.
- Medicines that suppress the immune system - such as prednisolone and ciclosporin may be effective but because of their potential side effects, their use is restricted to the most severely affected people.

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