Heat Rash

Medically Reviewed By William C. Lloyd III, MD, FACS
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What is heat rash?

Heat rash is one of many different types of rash. Rash is a symptom that causes the affected area to turn red and blotchy and swell. The rash may cause spots that are bumpy, scaly, flaky, or filled with pus. Rashes can vary in location, pattern and extent and may occur in any area of the body.

Heat rash, also called prickly heat or miliaria, occurs when sweat becomes trapped under your skin. Sweating is a self-regulating mechanism your body uses to maintain a constant temperature. Your sweat-producing glands are located in the middle layer of the epidermis, which is the outer layer of skin. If these glands become clogged and are unable to function, a rash may appear in the affected area. The rash may take one of several forms; it may be clear, skin-colored or reddened.

Heat rash can occur for a variety of reasons, such as wearing too much clothing or using blankets when hot. An individual’s anatomy can also lead to heat rash if there are folds or creases between areas of the skin where sweat can collect. Lotions and creams can clog the pores, along with the sweat glands, as well, producing heat rash.

The trapped sweat leads to the development of clear, raised bumps that indicate the areas of blockage. These bumps are usually not itchy if they occur as a result of a blockage toward the top layer of skin. Repeated or prolonged outbreaks can lead to an infection in the deeper layers of the epidermis and produce itchy, flesh-colored bumps.

Although heat rash itself is generally not serious, it may be a symptom of heat stroke, a life-threatening condition that, left untreated, can lead to organ failure. Seek immediate medical care (call 911) for serious symptoms, including high fever (higher than 101 degrees Fahrenheit); extreme thirst and dehydration; flushed appearance; weakness; rapid heart rate; shallow, rapid breathing; or changes in mental status, such as confusion or forgetfulness.

What are the symptoms of heat rash?

Symptoms of heat rash include the appearance of raised bumps on your skin in the affected area that may range in color from clear to red. The type and color of rash depend on the location in the skin where sweat glands are clogged, and symptoms have a range of severity. The mildest form is called miliaria crystalline (clear, raised rash), a blockage of the sweat glands at the top layer of the skin. Types that occur deeper in the skin include miliaria rubra (reddened rash) and miliaria profunda (larger and firmer bumps that are skin colored).

Common symptoms of miliaria cystallina heat rash

Common symptoms of heat rash originating in the outermost layer of the skin include:

  • Clear spots that break easily

  • Spots that do not produce itching or pain

Common symptoms of miliaria rubra heat rash

Common symptoms of heat rash originating in clogged pores in the epidermis include:

  • Red, raised spots

  • Spots that produce itching

Common symptoms of miliaria profunda heat rash

Common symptoms of heat rash originating in clogged pores in the dermis, or deep layer of the skin, include:

Serious symptoms that might indicate a life-threatening condition

Heat rash may be a symptom of heat stroke, a life-threatening condition that can lead to organ failure if untreated. Seek immediate medical care (call 911) if you, or someone you are with, have any of the following symptoms:

What causes heat rash?

Heat rash occurs when sweat becomes trapped under your skin.

Your sweat-producing glands are located in the middle layer of the epidermis. They can become clogged if you are wearing too much clothing (for example, when it is hot outside). Your anatomy can also predispose you to heat rash if you have folds or creases between areas of the skin where sweat can collect. Lotions and creams can clog the pores, along with the sweat glands, as well, producing heat rash.

What are the risk factors for heat rash?

A number of factors increase the risk of developing heat rash. Not all people with risk factors will get heat rash. Risk factors for heat rash include:

  • Excessive sweating

  • Hot, humid environments

  • Prolonged periods of inactivity, which permit sweat to collect and become trapped

  • Tight, constricting clothing that does not permit the skin to “breathe”

Reducing your risk of heat rash

Although you may not be able to control certain risk factors, such as living in a hot, humid climate, you can take some other steps to reduce your risk of heat rash.

You may be able to lower your risk of heat rash by:

  • Changing out of sweat-soaked clothing

  • Drinking plenty of water

  • Moving around to ensure sweat cannot collect in a certain area

  • Staying cool in hot weather by seeking shade or air-conditioned locations

  • Wearing loose clothing made with breathable fabrics such as cotton

How is heat rash treated?

The best way to treat heat rash is to ensure that you get plenty of air circulation around your skin. This means wearing light, loose clothing that will let your skin “breathe.” Staying cool and drinking lots of water can help minimize your symptoms and prevent heat rash from progressing to heat stroke.

Treatments for heat rash

If your heat rash does not resolve, some topical creams are available for treatment including:

  • Anhydrous lanolin, a lubricating ointment

  • Calamine lotion, which reduces itching

  • Steroid creams, which help clear the inflammation

What you can do to improve your heat rash

Self-care measures for treating heat rash include:

  • Drinking plenty of water

  • Eating fruits such as watermelon that have a high water content

  • Moving around to ensure air circulation around your body

  • Staying cool in hot weather by seeking shade or air-conditioned locations

  • Wearing loose clothing made with breathable fabrics such as cotton

What are the potential complications of heat rash?

Although heat rash itself is not serious, it can be associated with environmental conditions such as high temperatures that lead to serious complications such as heat stroke, which is a potentially life-threatening medical emergency. You can help minimize your risk of serious complications by following the treatment plan you and your health care professional design specifically for you. Complications associated with heat rash include:

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 10
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.
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