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.
What are the causes of heat rash?
It is uncertain why some people get heat rashes and others don’t.
The sweat gland ducts can become blocked if excessive sweating occurs, and that sweat is not allowed to evaporate from a specific area. Some examples of how blockage may occur include the following:
- Creases in the skin like the neck, armpit, or groin have skin touching adjacent skin, which makes it difficult for air to circulate, and prevents sweat evaporation.
- Tight clothing that prevents sweat evaporation.
- Bundling up in heavy clothing or sheets. This may occur when a person tries to keep warm in wintertime or when chilled because of an illness with fever.
- Heavy creams or lotions can clog sweat ducts.
- Babies have immature sweat glands that aren’t able to remove the sweat they produce. They can develop heat rash if they are exposed to warm weather, are overdressed, excessively bundled, or have a fever.
Heat rash may occur as a side effect of some medications (for example, isotretinoin [Accutane] or clonidine [Catapres]).
What are the symptoms of heat rash in children and adults?
The common symptoms of heat rash are red bumps on the skin, and an itchy or prickly feeling to the skin.
These are due to inflammation of the superficial layers of the skin (the epidermis) and the prickly sensation is similar to the feeling of mild sunburn.
The symptoms of heat rash are the same in infants and adults; however, since an infant can’t complain about the rash sensation, he or she may be fussy.
Who is at risk for heat rash?
Newborns, infants, the elderly, and obese individuals with large areas with skin-on-skin contact areas (for example, a large overlapping area of abdominal fat or panniculus) are at risk for developing heat rash.
They all are especially at risk if they are immobile for long periods of time and parts of the skin aren’t exposed to circulating air, which results in the inability of the sweat ducts to “breathe” (evaporative cooling).
Heat rashes are more common in places with hot, humid, climates because people sweat more.
Intense exercise associated with lots of sweating may cause a heat rash, especially if the clothing worn does not allow adequate air circulation.
What does heat rash look like?
The appearance of the heat rash depends upon where the excess sweat gets deposited in the skin.
Tiny blisters that look like small beads of sweat are seen if the sweat is blocked at the most superficial layers of the skin where the sweat duct opens on the skin surface.
Called miliaria crystalline, it has no symptoms other than these “sweat bubbles.”
Classic heat rash or miliaria rubra occurs if the sweat causes inflammation in the deeper layers of the epidermis. Like any other inflammation, the area becomes red (and therefore the name rubra = red) and the blisters become slightly larger.
Because the sweat glands are blocked and don’t deliver sweat to the skin’s surface, the area involved is dry and can be irritated, itchy, and sore. This rash is also called prickly heat.
How can I treat heat rash?
The most effective treatment for heat rash is to keep your skin cool and dry.
- Cool down. Avoid hot and humid places. If possible, stay in air-conditioned areas, or use fans to circulate the air. Use cool compresses to bring down the temperature of the affected skin.
- Dry off. Keep the irritated skin dry. Use a fan to dry the skin off faster and to reduce sweating.
- Reduce friction. Wear loose clothes to prevent irritation caused by clothing that rubs against the skin.
- Treat fever. If you have a fever, treat it with an over-the-counter drug, like acetaminophen (brand name: Tylenol) or ibuprofen (some brand names: Advil, Motrin), according to the directions on the package.
If your rash is severe, your doctor may prescribe a lotion to help relieve your pain or discomfort.
When should I go to the doctor?
In most cases, heat rash goes away on its own. If your heat rash doesn’t go away after 3 or 4 days, or if it seems to be getting worse, talk to your doctor.
In some cases, heat rash may be caused by an infection. See your doctor if your itchiness is severe or if the rash area swells or oozes pus. If you feel dizzy, nauseous, or confused, or you have trouble breathing, go to the emergency room right away.
These symptoms can be signs of serious heat-related illnesses, such as heat exhaustion or heatstroke.
How is heat rash diagnosed?
The diagnosis of heat rash or prickly heat is made by physical examination. Knowing that the rash appears during sweating or heat, appreciating the location on the body (in skin creases or where clothes fit tightly) and seeing what the rash looks like is enough to make the diagnosis.
As with many rashes, the health care professional may look at the involved skin and because of previous experience, immediately make the diagnosis.
How can I prevent heat rash?
In hot weather, dress yourself or your baby in lightweight cotton clothing. Cotton helps absorb moisture to keep it off of your skin.
If the weather is hot, turn on the air conditioner, or use a fan to help you stay cool and dry.
Avoid using baby powders and creams. They can block your pores and actually make your skin warmer.