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Which treatment is best for prickly heat?

QI have a patient who gets terrible 'prickly heat' when he goes in the sun abroad. He has tried various antihistamines without success. Can you tell me what causes prickly heat and any other treatments that may be appropriate? I think I have read somewhere that certain vitamins might be useful.

A'Prickly heat' or 'miliaria rubra' is caused by obstruction of the eccrine sweat duct in the epidermis. It is seen in environments that predispose to sweating, particularly hot and humid conditions.

Prickly heat affects up to 30 per cent of people in hot humid climates. It can begin within days of arrival and is maximal after two to five months, before a degree of acclimatisation occurs.

The rash appears on the flexures and at sites of occlusion or friction from clothing. Large numbers of tiny erythematous papules are seen, which produce an unpleasant prickly sensation.

The most important complications are infection and disturbance of heat regulation, the latter most often seen in young infants. Secondary bacterial infection may present as impetigo.

While antihistamines are arguably worth a try if it is difficult to avoid a tropical environment, the condition is not histamine mediated as far as we know.

In most cases the eruption settles rapidly once further sweating is avoided. Even a few hours per day in an air-conditioned room may be enough. Loose thin clothing should be worn, and irritants such as excessive soap should be avoided. Calamine lotion may be soothing but can be very drying. It may be followed by a bland emollient. Studies in the 1960s looked at the role of vitamin C in prickly heat but this has not been substantiated.

Dr Victoria Swale is a specialist registrar in dermatology at the Royal Free hospital, London

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