Sweat rash vs heat rash: What's the difference?

Why does sweat cause a rash?

Sweating is how your body cools itself. Sweating more in hot weather or during exercise is normal; sweating itself is not a skin disease. Heat rash develops when sweat cannot escape through the sweat ducts, the tiny channels that carry it to the skin's surface. Blockage and inflammation are the problem, not simply having sweat on your skin. Hot, humid conditions favour heat rash, and newborns and people in hospital are also commonly affected.134

What does heat rash look and feel like?

Look for small raised spots with itching, a prickly feeling or mild swelling. Some spots contain fluid. The rash looks red on white skin but can look grey or white, or be harder to see, on brown or black skin. Adults and children often have similar symptoms. Heat rash can appear anywhere and spread across the body, but it is not contagious.5

Heat rash often forms beneath clothing and in skin folds where airflow is limited. Common adult sites include the arms, back, chest and inner thighs. Babies often develop it around the neck, armpits, groin and upper chest or back. A milder form produces tiny clear bumps and can occur without itching.4

How do you treat sweat rash or heat rash?

1. 1Move somewhere cooler, ideally with air conditioning, and remove clothing covering the affected area.
2. 2Gently wash with cool or lukewarm water, then pat dry rather than scrubbing.
3. 3Leave the area uncovered where practical, or wear clean, loose cotton clothing that does not rub.
4. 4For prickling or itching, apply a cool damp cloth or a wrapped ice pack for up to 20 minutes.
5. 5Keep the skin cool while it heals. Limit activities that cause heavy sweating, and tap or pat instead of scratching.

Loose cotton clothing helps keep skin cool, without asking your wardrobe to double as a personal greenhouse.5

Should you put cream on it?

Cooling and airing the skin come first. Avoid products that block pores and trap sweat, and skip perfumed shower gels or creams. If itching needs treatment, ask a pharmacist about calamine lotion, antihistamine tablets or hydrocortisone cream. Children under 10 need a doctor's advice before using hydrocortisone. Do not automatically apply your usual moisturiser: products suitable for dry, itchy skin are not necessarily suitable for heat rash.456

What if the rash is under gloves or work equipment?

Sweating inside gloves can cause irritant contact dermatitis, meaning inflammation from skin irritation. Protective equipment can also irritate through rubbing or trigger an allergy to its materials. Separately, equipment that prevents sweat evaporation can cause overheating and heat rash. These problems need different responses; the location alone cannot identify the cause. Follow workplace safety protocols when removing equipment, and seek assessment if the cause is unclear.2

How long does it last, and when should you get help?

Heat rash usually improves within a few days. See a doctor if it does not improve, becomes painful or intensely itchy, or comes with fever, chills or warm, swollen skin. Get advice if you are worried about a baby's rash. Itching during pregnancy should be checked by a GP or midwife rather than assumed to be heat rash.456

Use lightweight bedding to keep skin cool at night, rather than giving the duvet a summer job it was not qualified for.5

In hot or humid weather, take frequent cooling breaks in air conditioning or shade. Heat exhaustion and heatstroke are different from heat rash and can be serious; do not push through symptoms of heat illness.7