Skin rash from sweat: what causes it and what helps

Why does sweating cause a rash?

Sweating is normal in hot weather and during exercise. Sweat cools the body as it evaporates; its job description does not include a spa detox. Your liver and kidneys do most of the work of removing toxins, so deliberately sweating more is not necessary to cleanse your body.56

Heat rash, also called miliaria or prickly heat, develops when sweat ducts become blocked or inflamed. Hot, humid weather, intense activity, fever and clothing that traps moisture increase the risk. Babies are particularly prone because their sweat ducts are immature. Adults can get it too, especially where clothing rubs or skin stays covered.1

What does heat rash look like?

Typical heat rash causes small raised spots, an itchy or prickly feeling and mild swelling. Some spots contain fluid. On white skin, the rash often looks red; on brown or black skin, the spots can look grey or white and be harder to see. Heat rash can spread across the body, but it is not contagious.4

In adults, heat rash commonly affects the upper body, scalp, neck and skin folds. In children, it often affects the body and folds around the neck, armpits or groin. Another form causes tiny, clear blisters near the skin surface that break easily. Appearance alone cannot reliably separate every sweat related rash from infections or other skin problems.1

What should you do first?

1. 1Move somewhere cooler. Use an air conditioned space or a cool, ventilated room, and pause activity that keeps you overheated.
2. 2Remove wet clothing and loosen tight layers. Wear loose cotton clothing and use lightweight bedding.
3. 3Cool the skin with a cool bath or shower. For local discomfort, apply a damp cold cloth or an ice pack wrapped in a towel for up to 20 minutes.
4. 4Pat or tap itchy skin rather than scratching. Avoid perfumed shower gels and creams, excessive soap and other irritants.
5. 5Drink plenty of fluid to avoid dehydration.

Loose clothing and lightweight bedding help keep skin cool, rather than asking your wardrobe and duvet to collaborate on a greenhouse.4

Which creams or medicines help?

Cooling is the main treatment for heat rash. A pharmacist can advise about calamine lotion, antihistamine tablets or hydrocortisone cream for discomfort. Children under 10 need a doctor's advice before using hydrocortisone. Calamine can be drying, so a moisturizer can be needed alongside it. An infected rash needs medical assessment and sometimes treatment for the infection.124

How long should it take to clear?

Most heat rash clears within a day or two after moving to a cooler environment, although it can take a few days. See a doctor if it is not improving after a few days. To reduce repeat episodes, keep your sleeping space cool, avoid excessive layers and remove wet clothing promptly.14

Could it be hives or eczema instead?

Cholinergic urticaria is not the same as blocked sweat ducts. Its mechanism is uncertain, and welts can occur without sweating. Repeated brief episodes during exercise or stress deserve assessment rather than automatically being treated as prickly heat.2

What if sweat triggers your hand or foot eczema?

If you have diagnosed dyshidrotic eczema, staying cool is only part of care. Use a fragrance free cream or ointment after washing and whenever skin feels dry. Lotions can worsen this form of eczema because they contain too much water. Wash gently with lukewarm water and a mild, fragrance free cleanser; avoid antibacterial and deodorant soaps.3

Remove rings before washing, moisturizing and sleeping, because irritation and moisture trapped beneath them can cause flares. For wet work, wear cotton gloves under waterproof gloves. Moisture wicking socks help keep affected feet dry. Avoid scratching and known irritants. If the trigger is unclear, a dermatologist can investigate allergies or irritation.3

When does a rash need medical help?

Seek immediate medical attention for a sudden rash that spreads quickly, trouble breathing or facial swelling. These can be signs of a dangerous allergic reaction.7

Contact a doctor if the rash has any of these features:

• Severe pain.
• Blisters, especially around the eyes, mouth or genitals.
• Yellow or green fluid, warmth or red streaks.
• Fever or constant itching.
• No improvement after a few days of heat rash care, or persistence after a week of rash treatment.
• A rash in your baby that worries you.

For a persistent or recurring rash, note where it appears, its triggers and any new soaps, creams or household products. A clinician will examine the skin and ask about exposures and medical history; testing can include allergy patch tests or tests for infection. Also mention changes in how much or how often you sweat.67