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 5/22/2014

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Heat rash condition

Heat-Related Illness Signs and Symptoms

How to Recognize a Heat-Related Illness Signs and Symptoms

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

  • Heat rash
  • Heat cramps
  • Heat syncope: Someone who experiences heat syncope (fainting) will experience the sudden onset of dizziness or fainting after exposure to high temperatures, particularly after exercising in the heat.
  • Heat exhaustion
  • Heat stroke

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