When it’s hot and humid, sweat glands can become blocked by excess perspiration, trapping sweat beneath the skin and causing a red, bumpy, prickly rash — heat rash. It’s more common among babies, whose sweat glands are immature, and among people who aren’t accustomed to heat and humidity, says Maral Skelsey, a clinical associate professor of dermatology at Georgetown University Medical School. Skelsey says tight-fitting clothing can further encourage the rash to develop by trapping sweat against the skin instead of allowing it to evaporate.
In babies, Skelsey says, the condition tends to resolve on its own; keeping a baby cool and lightly dressed — or even naked if the temperature is warm enough — is usually all that’s required. Adults, she says, may wish to treat the rash with over-the-counter topical steroid cream (to calm the itch), calamine lotion or anhydrous lanolin, an over-the-counter balm that can help keep skin ducts from getting blocked. Avoid getting overheated in the first place by taking breaks from outdoor heat in air-conditioned spaces when possible. As your body gets acclimated to summer’s hot and muggy weather, Skelsey adds, it will become less prone to heat rash.