Heat Rash

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Heat rash facts

  • Heat rash occurs when the skin's sweat glands are blocked and the sweat produced cannot get to the surface of the skin to evaporate. This causes inflammation that results in a rash.
  • The rash appears as reddened skin with tiny blisters and is due to inflammation. It often occurs in skin creases or areas of tight clothing where air cannot circulate.
  • The rash may be itchy or cause a prickly sensation and therefore it is also known as prickly heat.
  • Heat rash usually fades when the skin is allowed to cool. Medical treatment is necessary only if the area becomes infected.
  • Heat rash can be prevented by avoiding hot, humid conditions, wearing lose fitting clothes and using air conditioning or fans to allow air to circulate.

What is heat rash?

The skin's job is to protect the inside of the body from the outside world. It acts as a preventive barrier against intruders that cause infection, chemicals, or ultraviolet light from invading or damaging the body. It also plays an important role in the body's temperature control. One way that the body cools itself is by sweating, and allowing that sweat or perspiration to evaporate. Sweat is manufactured in sweat glands that line the entire body (except for a few small spots like fingernails, toenails, and the ear canal).

Sweat glands are located in the dermis or deep layer of the skin, and are regulated by the temperature control centers in the brain. Sweat from the gland gets to the surface of the skin by a duct.

A heat rash occurs when sweat ducts become clogged and the sweat can't get to the surface of the skin. Instead, it becomes trapped beneath the skin's surface causing a mild inflammation or rash.

Heat rash is also called prickly heat or miliaria.

Picture of the layers of the skin including the sweat glands
Picture of the layers of the skin including the sweat glands
Medically Reviewed by a Doctor on 5/20/2013

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Heat-Related Illness Signs and Symptoms

How to Recognize a Heat-Related Illness

During a heat wave, it's important to know and be able to recognize the signs and symptoms of a heat-related illness. There are different types of heat-related illnesses, ranging from those that cause temporary discomfort to the generally fatal condition known as heat stroke. In all heat-related illnesses, the symptoms appear when a person is exposed to extreme temperatures.

The following checklist can help you recognize the symptoms of heat-related illnesses:

Heat Rash: Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. It can occur at any age but is most common in young children. Heat rash looks like a red cluster of pimples or small blisters.

Heat cramps: A person who has been exercising or participating in other types of strenuous activity in the heat may develop painful muscle spasms in the arms, legs, or abdomen referred to as heat cramps. The body temperature is usually normal, and the skin will feel moist and cool, but sweaty.


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