Heat rash happens when sweat ducts, the tiny tubes that carry sweat to the skin surface, become blocked and trap sweat underneath. Hot, humid weather, exercise and clothing that traps heat and moisture can trigger it. Heat rash is also called sweat rash, prickly heat and miliaria, because even trapped sweat gets several names.23
What does itchy heat rash look like?
The common itchy type, miliaria rubra, causes small raised bumps, sometimes with fluid inside, and mild swelling. The rash looks red on white skin; on brown or black skin, spots can look grey or white and be harder to see. It often appears around the neck, upper chest, armpits, groin or skin folds, where sweat collects or clothing rubs. It can spread across the body, but you cannot pass it to another person.123
Another type, miliaria crystallina, produces tiny clear blisters that break easily, without inflammation. The deeper type, miliaria profunda, produces deeper bumps and can have no symptoms. Itching alone cannot identify heat rash: other rashes can itch and look similar. A doctor can examine an uncertain rash rather than relying on how itchy it feels.234
How do you calm the itching?
- 1Move somewhere cool and well ventilated, and change out of sweaty clothes. Reducing sweating is the main treatment, not just a way to make the rash feel better.
- 2Take a cool bath or shower. Wear loose cotton clothing and use lightweight bedding. Lightweight bedding helps keep skin cool, so the duvet does not need to attend every season.
- 3Hold a cool damp cloth against the rash, or use an ice pack wrapped in a tea towel, for up to 20 minutes.
- 4Pat or tap instead of scratching. Avoid perfumed shower gels and creams, and keep your nails short and smooth to reduce damage from scratching.
Can a cream or antihistamine help?
Calamine lotion can soothe discomfort, but it can also dry the skin. If your skin becomes dry, a gentle, unperfumed moisturiser can help. Ask a pharmacist whether calamine, an antihistamine tablet or hydrocortisone cream is suitable. Antihistamines help some causes of itching, not every cause. For children under 10, get a doctor's advice before using hydrocortisone. Severe rashes that do not improve can need prescribed treatment.12356
How long should it take to settle?
Most heat rash settles within a day or two after moving to a cooler environment, although it can take a few days. Keep skin cool and dry while it heals. See a doctor if it does not improve after a few days, covers a large area or keeps returning.123
What if a baby has heat rash?
Babies are more prone to heat rash because their sweat glands are not fully developed. Move your baby to a cooler room or shade, remove extra clothing or blankets, and change sweaty clothes and wet nappies regularly. Keep their skin clean and dry. Have a doctor check the rash if you are worried.13
When does an itchy rash need medical care?
Seek urgent care for pus, fever or signs of infection. Severe pain, warmth or red streaks also need medical assessment. Get emergency help for a sudden, rapidly spreading rash, trouble breathing or facial swelling. Arrange a doctor's appointment if itching is severe or disrupts daily life. During pregnancy, tell your doctor or midwife about itching rather than assuming it is heat rash.3457
Where this answer comes from
- 1Heat rash (prickly heat)nhs.uk
- 2Heat rash (Miliaria): Images, Causes, and Treatmentdermnetnz.org
- 3Heat rashhealthdirect.gov.au
- 4Rash Evaluation: MedlinePlus Medical Testmedlineplus.gov
- 5Itchy skinnhs.uk
- 6Heat and colddermnetnz.org
- 7Itching | Pruritus | Itchy skinmedlineplus.gov
