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How to handle heat rash

You’ve got a rash. You quickly rule out the usual suspects: You haven’t been gardening or hiking or even picnicking, so it’s probably not a plant irritant such as poison ivy; likewise, it’s probably not chiggers or ticks carrying Lyme disease; and you haven’t been swimming in a pond, which can harbor the parasite that causes swimmer’s itch.

Your rash may be coming from a hard-to-escape reality of summer: heat.

Heat rash occurs when the sweat glands are blocked by tiny blisters – they resemble small beads of sweat – that form on the skin.

Heat rash, called miliaria by doctors, can cause the skin to redden if the glands are blocked in a deeper layer of the skin. The skin can feel irritated and itchy, giving rise to another common term for the syndrome – prickly heat.

The chain of events is the same in heat rash as in eczema. They both start with staphylococcus bacteria living on the skin, says Herb Allen, a dermatologist and researcher at Drexel University in Philadelphia.

“It’s normal flora,” he says. “It’s on everybody.”

Sometimes the bacteria produce a substance that scientists call biofilm. “It used to be called slime,” Allen says. “It coats and protects bacteria.” Biofilm can also clog up sweat glands.

What makes staph bacteria produce biofilm? Salt and water – or sweat. The bacteria sense the salty wetness as a dangerous environment and throw out slime in defense. The slime can block your sweat glands and trigger a rapid immune response that causes an itchy rash.

This sequence – you sweat and then your sweat glands clog – is more likely to occur, Allen says, “when you have too much clothing on – or too-tight clothes – or have been lying still on hospital bedsheets. There’s no air flow.”

Fresh air, a breeze, air conditioning and fan-circulated air all help sweat evaporate and prevent heat rash. “Adequate ventilation is the key,” says Mary Sheu, medical director of the Johns Hopkins Dermatology & Cosmetic Center. To prevent miliaria, wear lightweight clothing - and less of it, Allen says.

Anyone can get heat rash.

If you do, a heavy-duty moisturizer, especially one containing lanolin, can provide relief, Allen says. Calamine lotion or cortisone cream can also help.

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