Heat Rash in Babies: How to Recognise, Treat, and Prevent It

Your baby's skin is smaller, but it traps heat just as well. Heat rash isn't an allergy — it's a signal that your baby is too hot.

Thailand's hot season — March through May — pushes outdoor temperatures past 38 °C. Heat rash (also called prickly heat or miliaria) becomes a top-of-the-list skin problem for babies during these months.

This guide draws on NHS [1], AAD [2] and Thailand's Department of Health [3] to help you tell heat rash from other rashes, treat it correctly at home, and know when to see a doctor.

What heat rash actually is

Skin has millions of sweat ducts. When your baby gets too hot, sweat tries to come out — but a baby's sweat ducts are still developing, and they clog easily. The trapped sweat forms tiny bumps under the skin. That's heat rash.

NHS [1] describes it precisely:

• Tiny 2–4 mm raised spots
• An itchy, prickly feeling like pins
• Mild swelling around the spots
• On lighter skin the rash looks red; on darker skin "it may be harder to see or look grey or white on brown or black skin"

Common locations on babies:

• Neck — folds collect sweat
• Chest and back — heavy clothing or thick swaddles trap heat
• Groin and armpit folds — air doesn't circulate
• Face — especially with a hat in a warm room

Telling heat rash apart from other rashes

The differences are usually clear once you know what to look for:

If you're not sure, cool your baby down for 24 hours. Heat rash improves visibly. Other rashes don't change.

Home treatment: cool, dry, loose

Heat rash treats easily, but you have to fix the cause, not just the symptom.

Cool

• Cool baths (room-temperature plain water) once or twice a day — not warm
• No scrubbing, no perfumed soaps
• Pat dry with a soft cloth — never rub
• NHS [1] recommends: a cool damp cloth or ice pack wrapped in a tea towel, applied for up to 20 minutes
• Plenty of fluids — under-6-month babies get this from breast milk or formula; over-6-month babies can have plain water in addition

Dry

• Pat sweat away often, especially in neck, groin, and armpit folds
• Change wet clothing immediately
• After a bath, leave the skin to air-dry for 1–2 minutes before dressing

Loose

• Light, loose cotton clothing in pale colours that reflect heat
• A thin cotton blanket instead of a heavy one
• Fan or AC in the bedroom
• One layer is usually enough — Thai babies are often dressed in one layer too many

What NOT to do

• No baby powder — it can be inhaled, and it may clog the very sweat ducts that are already blocked (NHS [1] advises avoiding perfumed products)
• No thick creams — they seal the skin and trap more sweat
• No hydrocortisone cream without a doctor's advice — NHS [1] is specific that pharmacist-suggested hydrocortisone is "not for children under 10"
• No fragranced products — they can trigger more inflammation
• No scrubbing with loofahs or rough cloths

When to see a doctor

Most heat rash clears in 2–3 days once the heat is managed. See a doctor if:

• The rash hasn't improved after 3–4 days of cooling care
• You see pus, broken skin, or oozing
• Your baby has a fever with the rash (fever + rash = consider infection)
• Your baby is very fussy and inconsolable
• The rash spreads quickly across the body
• Your baby is under 1 month old with any rash — always check first

NHS [1] puts it gently: "See a GP if you have heat rash that does not improve after a few days," and adds "your baby has a rash and you're worried." You don't have to wait for it to look bad.

Prevention for the Thai hot season

At home

• Run AC or fans, target room temperature 24–26 °C
• Don't let your baby sleep in direct sunlight
• Cotton sheets, not synthetic fibre

Outside

• Avoid going out 10 a.m. – 4 p.m. (the hottest window)
• Stroller canopy yes, but don't drape thick cloth over it — that traps heat
• Hat outdoors, off indoors — take it off when you come back in

One cotton layer is enough

Thai babies don't need the layered dressing that babies in cold climates do. A single onesie plus thin cotton trousers is usually enough in any room above 25 °C.

Summary

1. Heat rash is a signal that your baby is too hot
2. Cool, dry, loose are the three words that fix it
3. No baby powder, no thick creams — they make things worse
4. No hydrocortisone under 10 without a doctor
5. Improves in 2–3 days once the heat is managed
6. Fever + rash = doctor today

Heat rash isn't a disease — it's your baby telling you to cool things down. Adjust the room, adjust the layers, and most cases clear up at home.