Heat rash on the forearm: what helps?

What does heat rash look like?

Look for small raised spots, sometimes containing fluid, with itching, prickling or mild swelling. The spots often look red on white skin but can look grey or white on brown or black skin. Some forms produce tiny clear blisters instead. Heat rash can spread across the skin, but you cannot pass it to another person.34

Heat rash happens when sweat ducts, the tiny tubes carrying sweat to the skin surface, become blocked and sweat builds up underneath. Hot, humid weather, exercise and tight or heavy clothing make it more likely. A sweaty sleeve or clothing that rubs against the arm is a useful clue, not enough by itself to identify the rash.45

What should you do now?

1. 1Move somewhere cooler, ideally with air conditioning or good ventilation, and pause activities that make you sweat heavily.
2. 2Remove wet clothing. Gently wash your forearm with cool or lukewarm water, then pat it dry rather than scrubbing.
3. 3Leave the area uncovered where practical, or wear clean, loose cotton clothing that does not rub. Loose cotton clothing gives the skin airflow, a feature that does not need a trademark.
4. 4For prickling or itching, apply a cool damp cloth or an ice pack wrapped in a towel for up to 20 minutes.
5. 5Tap or pat itchy skin instead of scratching. Avoid perfumed shower gels and creams.

Do you need a cream?

Cooling and drying the skin usually come first, leaving an elaborate product lineup with surprisingly little to do. Avoid heavy creams, ointments or powders that trap sweat or block pores. If the skin is dry, ask a pharmacist about a suitable gentle moisturiser rather than layering several products over the rash.14

A pharmacist can advise whether calamine lotion, antihistamine tablets or hydrocortisone cream would help. Calamine can dry the skin. Get medical advice before using hydrocortisone on a child under 10. Severe rashes sometimes need prescribed treatment; pus or other infection signs need assessment rather than a stronger itch cream.345

How long should it take to clear?

Many cases settle within one or two days after moving to a cooler environment; others take a few days. See a doctor if the rash is not improving after a few days of cooling, covers a large area or keeps returning. To reduce repeat episodes, change sweaty clothing, take cooling breaks and keep sleeping spaces cool and ventilated.156

Could it be something else?

Consider recent contact with a new soap, lotion, detergent, plant or workplace chemical. Contact dermatitis means skin inflammation caused by an irritant or allergen, and it can also cause itchy bumps, blisters or dry, cracked skin. Tell a clinician about those exposures and any new medicines if the cause is unclear.12

When should you get medical help?

Get prompt medical advice for severe pain, intense itching, spreading warmth or swelling, pus, red streaks, fever or chills. Scratching can break the skin and allow infection. Seek emergency help for trouble breathing, facial swelling or a sudden rash that spreads quickly. Confusion, collapse or unusual behaviour after heat exposure can signal heatstroke, which is also an emergency. Heavy sweating with rapid breathing and a fast, weak pulse can indicate heat exhaustion rather than a skin rash alone.1267