Why do we get heat rash?

Why does sweat get trapped?

Normally, sweat travels through tiny tubes called sweat ducts, reaches the skin's surface and evaporates to cool your body. Heavy sweating can soften dead skin cells, making them more likely to clog those ducts. Sweat then backs up instead of escaping, causing inflammation. Skin debris and bacterial films can also contribute to blockage; trapped sweat can cause swelling that blocks the ducts further.23

Exercise, fever, tight clothing and dressings that seal the skin can encourage heat rash. People confined to bed can develop it where their skin rests against a waterproof mattress cover. Heat rash often appears beneath clothing or in skin folds where airflow is limited, so the wardrobe can have a supporting role nobody auditioned for. Anyone can get heat rash, regardless of age or skin colour.24

What does heat rash look like?

Typical symptoms are small raised spots, itching or prickling, and mild swelling. Some spots contain fluid. The rash often looks red on white skin, but grey or white on brown or black skin. Adults commonly develop it on the upper body, neck and areas rubbed by clothing. In children, the trunk and folds around the neck, armpits or groin are common sites. Heat rash is not contagious.14

The medical name is miliaria. Blockage near the surface produces tiny clear blisters that break easily, sometimes without itching. Deeper blockage causes the common itchy form called miliaria rubra. A rare, deeper form can follow repeated episodes. Not every rash triggered by warmth is heat rash: heat or exercise can also trigger hives that last just 15 to 30 minutes.345

How do you clear heat rash?

Cooling and airing the skin are the main treatment, which gives the bathroom shelf an unusually small role.2

1. 1Move somewhere cooler, preferably with air conditioning or ventilation, and remove clothing covering the rash.
2. 2Gently wash with cool or lukewarm water, then pat dry without scrubbing. Change out of wet clothing.
3. 3Leave the area uncovered where practical, or wear loose cotton clothing. Use lightweight bedding and keep the bedroom cool.
4. 4Soothe prickling with a cool damp cloth. If using an ice pack, wrap it in a towel and apply it for up to 20 minutes.
5. 5Pause activities that cause heavy sweating until the rash clears. Pat or tap rather than scratch, and avoid perfumed shower gels or creams.

Avoid thick creams, ointments and powders that can block sweat from escaping. If itching is troublesome, ask a pharmacist about calamine lotion, antihistamine tablets or hydrocortisone cream. Calamine can dry the skin. Children under 10 need a doctor's advice before using hydrocortisone.124

Why do babies get heat rash so easily?

Babies have immature sweat ducts and cannot control their temperature as well as older children and adults. Keep babies cool and dry, using lightweight, soft cotton clothing rather than extra layers. A fan can help if air conditioning is unavailable; position it far enough away to provide only a gentle breeze. Do not use baby powder to prevent or treat heat rash. Creams and ointments can keep their skin warmer and block pores.136

When does heat rash need medical attention?

Most cases settle within a day or two after moving to a cooler environment. See a doctor if the rash does not improve after a few days, becomes painful or intensely itchy, or keeps returning in your child. Seek care for possible infection if the skin becomes warm or swollen, or you develop fever or chills. Contact a doctor if your baby has a rash that worries you.124

Heat rash is usually harmless, but overheating can cause more serious illness. Heavy sweating with rapid breathing and a fast, weak pulse can signal heat exhaustion. Confusion, dizziness, nausea or a rapid, strong pulse in the heat can signal heat stroke and need immediate medical help.7