“They can both be red and itchy and sometimes they can occur in the same areas,” Dr. Katta added. “One difference is that eczema tends to look more patchy and scaly.” The itchy areas tend to be flatter and ill-defined at the edges, whereas heat rash tends to look and feel more like distinct bumps.
Another condition often mistaken for heat rash is polymorphous light eruption, which is an itching or burning rash of tiny, inflamed bumps or slightly raised patches of skin. “It’s a very unique condition that people notice when they take a sunny vacation,” for the first time in a while. It can happen any time, but often occurs when people travel in the spring or early summer and are exposed to much more sun than their bodies are used to, especially after the winter months, Dr. Lamb explained. This can cause them to “break out in a rash, usually pretty exclusively on the sun exposed areas.”
What’s unique about polymorphous light eruption though, she said, is that “unlike heat rash, it isn’t really due to temperature or humidity — it’s really due to sunlight.”
How do you treat and prevent it?
Experts say that anyone can get heat rash. If you develop it, or even if you have heat-induced eczema, the first thing you should do is move to a cooler location, Dr. Lamb said. Get out of the heat and into the shade, and avoid peak heat and humidity hours.
“Remove any tight fitting clothing” and wash off any thick lotions, like sunscreen or moisturizers, which might prevent your skin from breathing, Dr. Nadine Kaskas, a board-certified dermatologist at Mount Sinai, wrote in an email. “Take a cool shower or apply cool compresses with a clean washcloth.” She added that you can get over-the-counter ointments like calamine lotion to help soothe any itchiness — though if it becomes especially bothersome, you should consult with your doctor, as you may need a prescription for a topical steroid cream.
When left untreated, heat rash usually calms down on its own once you’ve gotten away from any hot and humid environments, Dr. Lamb said. Though there’s a slim chance of developing an infection if blisters break open and you do not keep your skin clean.