Prickly heat, also known as miliaria is an itchy rash of small, raised red spots that causes a stinging or prickling sensation on the skin. Miliaria is a common disorder of the eccrine sweat glands that often occurs in conditions of increased heat and humidity. Miliaria is thought to be caused by blockage of the sweat ducts, which results in the leakage of eccrine sweat into the epidermis or dermis (See Fig.1). The three types of miliaria are classified according to the level at which obstruction of the sweat duct occurs. In miliaria crystallina, ductal obstruction is most superficial, occurring in the stratum corneum. Clinically, this form of the disease produces tiny, fragile, clear vesicles. In miliaria rubra, obstruction occurs deeper within the epidermis and results in extremely pruritic erythematous papules. In miliaria profunda, ductal obstruction occurs at the dermal-epidermal junction. Sweat leaks into the papillary dermis and produces subtle asymptomatic flesh-colored papules. When pustules develop in lesions of miliaria rubra, the term miliaria pustulosa is used.
Prickly heat can develop anywhere on the body, but it usually appears on the face, neck, back, chest or thighs a few days after exposure to hot temperatures. The rash is made up of tiny spots or bumps that are surrounded by an area of red skin. The spots sometimes look like tiny blisters and can cause mild swelling, itching, and a stinging or intense prickling sensation.
Causes of Prickly Heat
Prickly heat usually develops when a person sweats more than usual, such as during hot or humid weather. However, it’s also possible to get prickly heat in the winter. The symptoms of prickly heat are usually worse in areas that are covered by clothing. This is because clothing can increase sweating and sometimes causes friction (rubbing). Babies and children are also more at risk of getting prickly heat because their sweat glands are not fully developed. The following also increase the risk:
- Illness and immobility – long periods spent in bed can increase sweating, particularly on warm bedding.
- Wearing too much clothing, particularly in the winter.
- Sitting too close to a fire or heater.
- Being overweight or obese – which is more likely to lead to excessive sweating.
Treating Prickly Heat
Prickly heat isn’t a serious condition and rarely requires any specific treatment. The rash usually disappears after a few days. However, to ease out the symptoms:
- Avoid excessive heat and humidity.
- Drink plenty of fluids to avoid dehydration, especially in hot weather.
- Wear loose cotton clothing – avoid wearing synthetic fibers, such as polyester and nylon, which trap heat easier than natural fibers.
- Keep skin cool by bathing that would soothe skin and help to prevent further sweating. Staying in an air-conditioned room for a few hours a day will also provide considerable relief. A cold compress may also be effective, but should not be left on the skin for longer than 20 minutes.
- Use calamine lotion to soothe sore and irritated skin.
- Low-strength hydrocortisone cream is also effective in treating very itchy and irritated areas of skin. However, avoid using it on the face.
- An antihistamine may help to control itching, but consultation with a physician is advisable as they are not always suitable.
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