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What is a Heat Rash?

By HERWriter
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treatment for heat rash Goodshoot/Thinkstock

It is a hot, humid day and you notice as you run your hand over your shoulder, a bumpy mild rash has erupted. It is likely the rash is a heat rash, also known as prickly heat or miliaria.

Heat rashes develop when perspiration become trapped due to blocked pores or sweat glands. Common places for heat rashes to occur are the groin, neck, under the breasts and armpits.

The rash can range from mild, clear, fluid-filled blisters to a red, itchy, bumpy rash as in this photo.

Types of heat rashes:

Miliaria crystallina:
This is the mildest type of heat rash and forms small fluid-filled blisters that are not painful or itchy. It only affects sweat glands on the surface of the skin. Newborns can get this type due to their immature sweat gland development but so can adults.

Miliaria rubra:
This is the most common type and is also called prickly heat due to the itchy sensation that accompanies the rash. The rash occurs in the deeper layer of the epidermis so it's reddened and bumpy. Adults, children and older infants can develop this type and occasionally a bump can become infected and fill with pus.

Miliaria profunda:
This type primarily occurs to adults who have had repeated bouts of miliaria rubra. The bumps are larger, harder and skin-colored and may start as soon as the person begins to exercise.

This type of heat rash can be more dangerous if a large area of skin is involved due to the person’s inability to sweat. They should be watched so that they do not develop other heat related complications such as heat cramps or heat exhaustion.


- Remove constricting clothing and allow more air to flow around the area that has the rash.

- Move the person inside to an air-conditioned environment or in front of a fan, which will cool the skin through evaporation.

- Calamine can be used to soothe the itch of the rash.

- Topical steroids can be used if the rash is more severe.

Heat rashes usually resolves on their own but if the rash becomes worse or the person develops any symptoms of being excessively over-heated such as confusion or nausea, then medical attention should be sought.


- Avoid wearing certain fabrics that don’t breathe or wick away sweat. Take care not to overdress infants and children.

- Avoid using heavy creams and ointments or baby powder which can block the pores.

- Take daily showers after exercise.

- Take time to monitor your skin for the appearance of a rash when doing physical activity that makes you sweat a lot more, or when in more humid tropical environments.

- Be sure to drink enough water to replace fluids lost, especially if it is hot and humid or during exercise.


Heat rash. MayoClinic. Web. May 6, 2012.

Heat Rash. MedicineNet.com. Web. May 6, 2012.

Heat Rash. Pediatric Dermatology Basics By Vincent Iannelli, M.D., About.com Guide. Web. May 6, 2012.

HEAT RASH. FamilyDoctor.org. Web. May 6, 2012.

Michele is an R.N. freelance writer with a special interest in woman’s healthcare and quality of care issues. Other articles by Michele are at www.helium.com/users/487540/show_articles

Edited by Jody Smith

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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.