Prickly heat is a common disorder of the sweat glands characterized by a red, itching, prickling rash following exposure to high environmental temperatures.
Prickly heat is also known as heat rash, sweat retention syndrome, and miliaria rubra. This disorder occurs during the summer months or year-round in hot, humid climates, and is caused by blockage of the sweat glands. The skin contains two types of glands: one produces oil and the other produces sweat. The sweat glands are coil-shaped and extend deep into the skin. Blockage can occur at several different depths, producing four distinct skin rashes:
- Miliaria crystallina. This is the most superficial blockage and affects only the thin upper layer of skin, the epidermis. Sweat that cannot escape to the surface forms little blisters. A bad sunburn as it just starts to blister can look exactly like miliaria crystallina.
- Miliaria rubra. Blockage at a deeper layer causes sweat to seep into the living layers of skin, causing irritation and itching.
- Miliaria pustulosais. A complication of miliaria rubra in which the sweat is infected with pyogenic (pus-producing) bacteria and contains pus.
- Miliaria profunda. The deepest of all blockages causes dry skin and possibly goose bumps.
These four types of heat rash can cause complications because they prevent sweat from cooling the body, as normally occurs when the sweat evaporates from the skin surface. Sweating is the most important human cooling mechanism available in hot environments. If it does not work effectively, the body can rapidly become over-heated, with severe and potentially fatal consequences.
Causes & symptoms
The best evidence to date suggests that bacteria form the plugs in the sweat glands. These bacteria are probably normal inhabitants of the skin, and why they suddenly interfere with the free flow of sweat is not understood.
Heat rash appears suddenly and has a hot, itching, prickling sensation. Infants are more likely to get miliaria rubra than adults. Obese persons are also more susceptible to heat rash. All the sweat retention rashes are also more likely to occur in hot, humid weather.
Failure to secrete sweat can cause the body to overheat. Before the patient suffers heat stroke, there will be a period of heat exhaustion symptoms (dizziness, thirst, weakness) when the body is still effectively maintaining its normal temperature. Then the patient's temperature rises, often rapidly, to 104 or 105° F (40° C) and beyond. Heat stroke is an emergency that requires immediate and rapid cooling. The best method of treatment is immersion in ice water.
Naturopaths maintain that essential fatty acids can speed the clearing of the rash. The patient should eat fish rich in fatty acids (salmon, mackerel, or herring). Other sources include dark green leafy vegetables and flaxseed oil.
The homeopathic remedy for prickly heat is a dose of apis in 30c potency, taken when the itching or prickling sensation begins. Apis may be taken every 2 hours for up to 10 days.
Herbal treatments to relieve itching include sprinkling arrow root powder over the rash or rubbing a slice of fresh daikon radish or raw potato over the rash. A sponge bath with ginger will increase circulation. Fresh grated ginger is steeped in boiling-hot water, cooled, and then sponged over the rash. For widespread itching the patient can take cool baths with corn starch and/or oatmeal.
Chinese herbal medicines are used internally for widespread prickly heat or externally for small areas of rash. The medicines Zhi Yang Po Fen (Relieve Itching Powder), Jie Du Cha Ji (Resolve Toxin Smearing Liquid), and Qing Dai San Cha Ji (Natural Indigo Powder Smearing Liquid) can be applied to the rash. Fresh lotus leaf with a decoction of Jin Yin Hua (Flos lonicerae) can be taken as a tea. A decoction of the following herbs can be taken by mouth:
- Qing Hao (Herba artemisiae annuae): 5g
- Bo He (Herba menthae): 5 g
- Jin Yin Hua (Flos lonicerae): 10 g
- Dan Zhu Ye (Herba lophatheri): 10 g
- Lu Dou Yi (Pericarpium phaseoli munginis): 10 g
- Ju Hua (Flos chrysanthemi): 5 g
- fresh lotus leaf: one piece
Heat rash may be treated with topical antipruritics (itch relievers) containing calamine, aloe, menthol, camphor, eucalyptus oil, and similar ingredients. Dermatologists can peel off the upper layers of skin using a special ultraviolet light. This treatment will remove the plugs and restore sweating, but is not necessary in most cases.
Because the body cannot cool itself adequately without sweating, careful monitoring for symptoms of heat exhaustion is important, especially in infants or the elderly. If the symptoms of heat exhaustion do appear, the person should move into the shade or take a cool bath or shower. Clinical studies have found that application of topical antiseptics like hexachlorophene almost completely prevented these rashes. General measures to prevent prickly heat include:
- wearing loose-fitting clothing
- removing sweat-soaked clothing
- taking a cool shower or bath after sweating
- limiting outdoor activities to the mornings and evenings during hot weather
- staying in an air-conditioned environment during hot weather.
Berger, Timothy G. "Skin and Appendages." In Current Medical Diagnosis and Treatment, edited by Lawrence M. Tierney, Jr., et al. Stamford, CT: Appleton & Lange, 1996.
"Sweat Retention Syndrome." In Dermatology in General Medicine, edited by Thomas B. Fitzpatrick et al. New York: McGraw-Hill, 1993.
Ying, Zhou Zhong, and Jin Hui De. "Prickly Heat and Summer Dermatitis." Clinical Manual of Chinese Herbal Medicine and Acupuncture. New York: Churchill Livingston, 1997.