Signs of Heat Rash

The Skin's Function

The body cools itself is by sweating, and allowing that sweat or perspiration to evaporate.

Your skin is your first line of defense from the outside world. It protects you from infections, chemical exposures, and harmful ultraviolet light. It also helps regulate the temperature inside your body by producing sweat. Sweat on your skin comes from sweat glands located all over your body (except in your fingers, toenails, and ear canals). These small glands are regulated by the brain and produce sweat that comes to the surface via ducts on your skin, which then evaporates and helps cool you down.

What Is Heat Rash?

Picture of clogged sweat ducts, which causes heat rash.

Heat rash (prickly heat or miliaria) is a mild inflammation of clogged sweat ducts. When the sweat ducts are blocked the sweat cannot come to the skin surface to evaporate and becomes trapped under the skin. The rash is characterized by small, raised bumps (like coarse sandpaper) spread evenly across small patches of skin. The rash usually goes away on it's own and resolves in hours to a few days.

What Are the Symptoms of Heat Rash in Children and Adults?

Common symptoms of heat rash are red bumps on the skin, and an itchy or prickly feeling to the skin.

The common symptoms of heat rash include a fine, bumpy, itchy rash, skin burning, and a "prickly" feeling (like something is crawling on skin). The most common body parts affected are areas commonly exposed to the sun such as the hands, face, neck, and elbow folds. Heat rash may also affect areas covered by tight clothing such as the abdominal wall, groin, thigh creases, buttocks, and the area under the breasts.

Heat Rash Types

There are four types of heat rash; clear (miliaria crystalline), red (miliaria rubra), white/yellow (miliaria pustulosa) and deep (miliaria profunda).

The four types of heat rash (miliaria) are named by the way they look on the skin (visual characteristics) and are discussed on the following slides:

  1. Clear (miliaria crystallina),
  2. Red (miliaria rubra),
  3. White/Yellow (miliaria pustulosa),
  4. Deep (miliaria profunda).

Clear Heat Rash (Miliaria Crystallina)

Picture of a clear heat rash (miliaria crystalline).

Miliaria crystallina, or clear heat rash, looks like small, clear beads of sweat on the top layer of skin. It is usually very mild and doesn't produce many uncomfortable symptoms.

Red Heat Rash (Miliaria Rubra)

Picture of red heat rash (miliaria rubra), also known as prickly heat.

Red heat rash (miliaria rubra) is the most common form of heat rash. This type is also called "prickly heat" because of its intense itching and burning symptoms. The sweat glands are blocked and the inflammation causes a red color to the rash known as "rubra" (hence the name miliaria rubra).

White/Yellow Heat Rash (Miliaria Pustulosa)

Picture of white/yellow heat rash (miliaria pustulosa).

When pustules form on a case of red heat rash it is called white/yellow heat rash (miliaria pustulosa). These pustules may be the first signs of a skin infection and should be checked by your doctor.

Deep Heat Rash (Miliaria Profunda)

Picture of deep heat rash (miliaria profunda).

With repeated episodes of heat rash, sweat glands in larger areas of the skin may be chronically inflamed and cause damage to deeper layers of the skin. When this happens, large, firm bumps may appear especially after exercise or exposure to heat. This is called deep heat rash (miliaria profunda).

What Are the Causes of Heat Rash?

Heat rash can be caused by various factors including creases in the skin, tight or heavy clothing, heavy creams and lotions, and the side effect of medications.

Blocked sweat glands are the main cause of heat rash. Sweat glands can get blocked for many reasons but the most common reasons include:

  • Skin around the neck, armpit, or groin that touches or rubs adjacent skin prevents sweat evaporation.
  • Tight clothing around the waist, abdomen, chest, or groin that prevents evaporation of sweat.
  • Bundling up in heavy clothing where sweat can accumulate on the skin.
  • Heavy creams, oily lotions, or adhesive bandages can clog sweat ducts.

Who Is At Risk for Heat Rash?

Newborns, infants, and the elderly are at risk for developing heat rash.

Some situations can make heat rash more likely, these include:

  • Newborns or infants (especially wearing diapers or tight-fitting clothes)
  • Elderly people who may not realize how much they are sweating or don't frequently change their clothes
  • Living in hot and humid climates
  • Working in hot, confined spaces where sweat is prevalent

Why Are Babies So Prone to Heat Rash?

Babies are more prone to heat rash due to immature sweat glands that aren't able to get rid of all the sweat they produce.

Small children frequently get heat rash because their sweat glands are immature and they cannot get rid of the sweat they produce. This is common when children are overdressed, bundled up for cold weather, or have a fever.

How Is Heat Rash Diagnosed?

The diagnosis of heat rash is made by physical examination.

The diagnosis of heat rash is made by seeing the characteristic rash in certain common skin locations, especially after known heat exposure. A doctor can usually make the diagnosis with a visual examination of the rash. However, complicated or atypical cases may need confirmation from skin culture, skin scrapings, or biopsy. Other skin conditions can mimic a heat rash including allergic reactions, bacterial infections, fungal infections, or eczema.

Home Remedy Treatments for Heat Rash

Heat rash often resolves on its own, but some home treatments can help including calamine lotion and over-the-counter hydrocortisone creams or sprays.

Heat rash is usually self-limited, meaning it resolves on its own without treatment. Over-the-counter treatments such as calamine, hydrocortisone cream, itch preparations (such as Benadryl spray), or sunburn lotions can be used to treat the itching and burning symptoms.. Excessive use of heavy creams or lotions may make the heat rash worse.

Medical Treatment for Heat Rash

If heat rash does not resolve on its own and/or becomes infected, antibiotic treatment may be required.

Occasionally the heat rash may get infected, especially if it has been scratched open. Bacteria can invade the skin and cause cellulitisinfections. Symptoms such as redness, swelling, increased pain, fever, or pustules should be checked by your doctor. Antibiotic treatment with topical creams or medications taken by mouth may be necessary to treat infections associated with heat rash.

How Can Heat Rash Be Prevented?

Heat rash can be prevented by allowing the skin to be exposed to circulating air and decreasing the potential for sweat glands to become inflamed.

Keeping sweat glands from becoming clogged is the best way to prevent heat rash. Wear loose-fitting and breathable clothing. Avoid exercising in hot, humid weather. Keep skin dry, especially areas like skin folds or creases where sweat can accumulate. Stay in air conditioning whenever possible if you are prone to heat rash.

How to Protect Yourself When Temperatures Are Extremely High

To avoid heat-related illnesses take frequent breaks to get out of the heat, and drink plenty of fluids to replenish fluid lost via sweat.

To an extent, your body can acclimate to hot and humid weather over time. Try to avoid working or exercising during times of extreme heat. Take frequent cooling breaks, drink plenty of fluids, and stop activities if you feel over-heated, lightheaded, dizzy, or faint.

Before exercise in hot and humid climates take into account the temperature and also the heat index. The heat index is a calculated measurement of the overall feeling of heat and humidity. Since sweat cannot evaporate if the water content in the air (humidity) is high, sweating alone cannot cool the body.

How Much Water Should I Drink in Hot Weather?

In a hot environment, a person should drink enough water to make the urine clear, and make sure the body is producing sweat.

It is hard to tell if you are dehydrated and need to drink more water just by how much you sweat. If you are dehydrated, your kidneys will try to retain as much water in your body as possible. This results in decreased urine output and the urine you do eliminate may be dark or concentrated. In hot environments, a good rule of thumb is to drink enough liquids to make your urine appear clear or just slightly yellow.

Should I Take Salt Tablets During Hot Weather?

Drink water and sports drinks (Powerade, Gatorade) to resupply the body with electrolytes as opposed to salt tablets in hot weather.

Do not take salt tablets to replace your electrolytes when you sweat excessively. They may be harmful or replace too much sodium, which may cause problems with your blood pressure, kidneys or heart. Plain water will help hydrate best.

What Is the Best Clothing for Hot Weather or a Heat Wave?

Lightweight, loose clothing allows air circulation to the body's surface and helps promote cooling during hot weather.

Sweating cools the body by evaporation which pulls heat away from your skin. If sweat is not allowed to evaporate due to tight clothing or certain non-breathable fabrics, this leaves you at risk to overheat or get a heat rash. Wear clothes made of fabrics such as cotton or synthetic fabrics designed to "wick" sweat away from skin to help it evaporate when you work out or expect to be exposed to heat.



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  • Centers for Disease Control and Prevention (CDC): "Heat Stress."
  • Family Doctor: "Heat Rash Overview."
  • UpToDate: "Patient Information: Heat Rash (Prickly Heat) (The Basics)."
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