Prickly heat is also known as sweat retention syndrome or miliaria rubra. It is a common disorder of the sweat glands.
The skin contains two types of glands. One type produces oil and the other produces sweat. Sweat glands are coil-shaped and extend deep into the skin. They are capable of plugging up at several different depths, producing four distinct skin rashes .
- Miliaria crystallina is the most superficial of the occlusions. At this level, only the thin upper layer of skin is affected. Little blisters of sweat that cannot escape to the surface form. A bad sunburn as it just starts to blister can look exactly like this condition.
- Deeper plugging causes miliaria rubra as the sweat seeps into the living layers of skin, where it irritates and itches.
- Miliaria pustulosis (a complication of miliaria rubra) occurs when the sweat is infected with pyogenic bacteria and turns to pus.
- Deeper still is miliaria profunda. The skin is dry and goose bumps may or may not appear.
There are two requirements for each of these phases of sweat retention: hot enough weather to induce sweating, and failure of the sweat to reach the surface.
Infants are more likely to get miliaria rubra than adults. All the sweat retention rashes are also more likely to occur in hot, humid weather.
Causes and symptoms
As of 2004, the best evidence suggested that bacteria form the plugs in the sweat glands. These bacteria are probably normal inhabitants of the skin, and why they suddenly interfere with sweat flow is still not known.
Besides itching , these conditions prevent sweat from cooling the body, which it is supposed to do by evaporating from the skin surface. Sweating is the most important cooling mechanism available in hot environments. If it does not work effectively, the body can rapidly become too hot.
When to call the doctor
A doctor should be called when an infant's temperature rises above 100°F (37.8°C) and cannot be brought down within a few minutes. Infants whose temperatures exceed 102°F (38.9°:C) should be immersed in tepid or lukewarm water to reduce body temperature slowly.
A physician should be notified if a baby becomes dehydrated. Signs of dehydration include lethargy, poor skin tone, generalized weakness, and reduced urination.
Rash and dry skin in hot weather are usually sufficient to diagnose these conditions.
The rash itself may be treated with topical antipruritics (itch relievers). Preparations containing aloe, menthol, camphor, eucalyptus oil, and similar ingredients are available commercially. Even more effective, particularly for widespread itching in hot weather, are tepid baths with corn starch and/or oatmeal (about 0.5 lb [224 g] of each per bathtub-full).
Dermatologists can peel off the upper layers of skin using a special ultraviolet light. This procedure removes the plugs and restores sweating but is not necessary in most cases.
Much more important, however, is to realize that the body cannot cool itself adequately without sweating. Careful monitoring for symptoms of heat disease is important. If they appear, some decrease in the ambient temperature must be achieved by moving to the shade, taking a tepid bath or shower, or turning up the air conditioner.
The rash disappears in a day with cooler temperatures, but the skin may not recover its ability to sweat for two weeks—the time needed to replace the top layers of skin with new growth from below.
Experimental application of topical antiseptics such as hexachlorophene almost completely prevent the rashes of prickly heat. Parents should consult their doctors before applying such antiseptics to their child's skin.
Babies should receive adequate water and other liquids during periods of high heat. They should consume adequate amounts of electrolytes such as sodium, chloride, potassium, phosphate and bicarbonate during hot weather.
A physician should be notified if a baby becomes dehydrated. Signs of dehydration include lethargy, poor skin tone, and generalized weakness. If oral replacement of fluid and electrolytes is suggested, then commercial or homemade preparations can be used. Commercial preparations such as Pedialyte are available. The World Health Organization has provided the following recipe for home preparation, which can be administered in small, frequent sips:
- table salt, 3/4 tsp
- baking powder, 1 tsp
- orange juice, 1 cup
- water, 1 quart
Parents should carefully monitor their young children for symptoms of heat disease. Babies should be carefully bathed to maintain normal sweating, especially during periods of hot weather.
Pyogenic —Capable of generating pus. Streptococcus , Staphocococcus , and bowel bacteria are the primary pyogenic organisms.
Syndrome —A group of signs and symptoms that collectively characterize a disease or disorder.
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L. Fleming Fallon, Jr., MD, DrPH