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Heat Rash or Prickly Heat (Miliaria Rubra)
Heat rash (miliaria rubra), also known as prickly heat, is a rash of small red bumps caused by blockage of the sweat glands. It can be due to high fever, excessive sweating, or being over-bundled. It is commonly seen in hot, humid tropical climates. It can cause discomfort, itching, and, sometimes, stinging or “prickly”-type pain.
Who's At Risk?
Heat rash is more common in hot, humid tropical climates. Someone who is new to such an environment is especially vulnerable. Heat rash can be due to high fever, excessive sweating, or being over-bundled. It occurs in individuals of all races, although to a lesser degree in Asians. Infants are the most commonly affected as they are subject to over-bundling out of concern for heat loss after birth.
Signs & Symptoms
Heat rash can occur after exposure to hot conditions. There can be many small, red bumps all over the body. The bumps of heat rash usually occur in highest concentration in covered areas where there is a lot of friction, such as the neck, chest, and body folds. The face, palms, and soles are generally not affected by heat rash. The rash can cause intense itching and stinging, which can become worsened by heat. The individual may feel fatigued and become intolerant of heat because of little or no sweating at the affected areas.
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Prevention and treatment of heat rash consist of controlling heat and humidity. Acetaminophen or ibuprofen can help to reduce fever, which can be a causative agent in the development of the rash. Remove any occlusive clothing, limit activity, and seek air conditioning or any cooler environment. Cool compresses can also help with the discomfort. Heat rash usually resolves once people move to a cooler environment. Make sure to drink lots of fluids.
If there are signs of secondary bacterial skin infection associated with the heat rash or otherwise, oral or topical antibiotics may be given.
Dehydration may be treated with intravenous fluids, especially if there is vomiting. Heat stroke is treated by trying to quickly reduce the core temperature to normal. Immersion, evaporative, or invasive cooling techniques may be used in addition to rapid administration of intravenous fluids. This type of care is administered within a hospital setting.
The most common complications from heat rash include secondary infection from scratching and heat exhaustion.
Although uncommon, infected areas due to breaks in the skin caused by scratching may need antibiotic treatment for resolution. Seek care if the rash develops pus, redness, crusting, swelling, or tenderness.
In cases of heat exhaustion, the skin will appear hot and flushed without any sweat. The person may complain of dizziness, nausea, weakness, headache, confusion, or difficulty breathing. Heat exhaustion can progress to heat stroke, so medical care should be obtained right away. Symptoms of heat stroke include a very high temperature of 105°F or greater, decreased or loss of consciousness, or seizure.
While awaiting medical care, get the affected person indoors or under shade, undress them, and apply cool compresses to the body.
>Bolognia, Jean L., ed. Dermatology, pp. 510, 578-579. New York: Mosby, 2003.
Wolff, Klaus, ed. Fitzpatrick’s Dermatology in General Medicine. 7th ed, p. 730. New York: McGraw-Hill, 2008.