Heat rash is a common skin problem in the summer, when sweat gets trapped underneath your skin. Heat rash on adults strikes in areas where your skin folds over itself, such as the armpits, groin and beneath the breasts.
“Sweat is the way the body cools itself, but at the same time too much sweating or sweat trapped below the skin can be irritating,” Anne Chapas, MD, a member of the American Academy of Dermatology and a board-certified dermatologist based in New York City, told TODAY.
Heat rashes on babies can develop when they are overly swaddled, since their immature sweat glands aren’t fully formed, so moisture can’t evaporate as well as it can in adults.
Symptoms of heat rash
What does heat rash look like? Most of the time, when you get a heat rash you’ll have small, itchy red bumps and blotches. Sometimes, you can get fluid-filled sacs. Heat rash usually comes on quickly —within hours after you get hot and sweaty.
It’s important not to scratch your heat rash, since scratching can damage the skin and introduce bacteria that can cause an infection.
Causes of heat rash
You can develop a heat rash when your sweat glands get blocked. “When there’s too much heat and humidity the sweat glands can clog up,” Danny Del Campo, MD, a member of the American Academy of Dermatology and a board-certified dermatologist based in Chicago, told TODAY. “You’re sweating so much, and your skin can’t breathe.” Your body tries to pump out more sweat, but it can’t, so you develop an inflammatory state with redness and sometimes goosebumps and blisters.
“We’re all sweating, especially if we’re working out. It’s easy to get heat rash in places where skin touches other skin,” Anthony Rossi, MD, a member of the American Academy of Dermatology and a board-certified dermatologist based in New York City, told TODAY.
Preventing heat rash
You’re less likely to develop a heat rash if you stay cool and dry. If you’re exercising, wear clothing that wicks away sweat so you’re not trapping sweat against your skin. Cotton doesn’t irritate your skin, but it doesn’t wick away moisture either. “Newer sports fabrics do a good job of wicking moisture away, but they are very compressing against skin. If you leave them on too long you can break out in a heat rash,” Dr. Rossi said.
Keeping your skin cool and dry is key. “The most important thing is to change out of those sweaty clothes quickly,” Dr. Chapas said. “Take a cool shower to cool down your body and change into a clean shirt.”
You can use antifungal powders, especially in your groin folds and armpits, to help absorb moisture.
Diagnosing and treating heat rash
If you’ve been sweating a lot and you develop a rash in your skin folds soon after, it’s likely heat rash.
For heat rash treatment, try to stay in a well-ventilated, air-conditioned place. Cool compresses and cool or lukewarm showers can help. To get rid of a heat rash, you can treat it at home with moisturizers, anti-inflammatory lotions like calamine lotion, and over-the-counter steroid creams.
Dr. Del Campo recommends putting your lotion or moisturizer in the refrigerator for treating heat rash. “When we put it on cold it feels better,” he said.
How long does heat rash last? Heat rashes typically go away within a day or so, though if they develop pimples, they could take a few days to clear. If your rash isn’t getting better in a few days, see a doctor. A rash that’s not clearing up could be another type of rash, bug bites or a viral infection. “If your rash isn’t associated with sweating or is spreading to other parts of your body like your chest, back or legs, it could be something else,” Dr. Chapas said.
Heat rash can also be a warning sign that you’re overdoing it in the warm weather. Don’t ignore it—overheating can also lead to heat stroke and heat exhaustion. And too much time in the sun can cause sunburn and sun poisoning.