Heat rash (prickly heat) in Thailand: what helps and when to see a doctor
Heat rash in Thailand is very common and usually harmless: small, itchy, prickly spots where sweat gets trapped under the skin. Keep the skin cool and dry and it normally settles by itself within a few days. This guide explains how to tell it apart from other rashes, what helps, and when a rash needs a doctor.
The short version
Heat rash in five points
- What it looks like: small raised spots with an itchy, prickly feeling, often on the neck, chest, back, armpits or where clothes rub.
- Cool the skin: shade, air conditioning or a fan, cool showers and loose cotton clothing.
- Don’t scratch: pat or tap the itch instead, and skip perfumed shower gels and creams.
- Ask a pharmacist if the itch is bothering you. They can suggest something suitable.
- See a doctor if it doesn’t improve after a few days, looks infected, or comes with a fever.
What is heat rash, and why is it so common in Thailand?
Heat rash, also called prickly heat or sweat rash, happens when you sweat a lot and the tiny sweat ducts in your skin get blocked. The trapped sweat irritates the skin and a rash appears, often a few days into a hot spell. It can’t be passed on to other people.
Southern Thailand is hot and humid all year, and on Koh Phi Phi most visitors spend their days sweating: walking the village lanes, climbing to the viewpoint, sitting on a boat in the sun or sleeping in a room without air conditioning. Humid air keeps sweat sitting on the skin instead of evaporating, which is exactly what heat rash needs. Sunscreen, tight swimwear and damp clothes worn for hours can make it worse.
How to recognise heat rash
According to the NHS, the symptoms of heat rash are small raised spots, an itchy or prickly feeling and mild swelling. The spots are about 2mm to 4mm across, and some may be filled with fluid. On white skin the rash looks red; on brown or black skin it can be harder to see and may look grey or white.
Typical places are areas that sweat and rub: the neck, chest and back, under the arms and breasts, the groin, inside the elbows and wherever a strap, waistband or backpack sits. The rash may spread, but it usually stays in sweaty areas and the person otherwise feels well.
Not every rash in Thailand is heat rash. Sunburn is hot, tender skin in the places the sun reached; our sunburn guide covers that. Insect bites are usually scattered, separate lumps. A rash that comes with a fever, or that spreads fast, needs a doctor rather than a guess.
Heat rash treatment in Thailand: what helps
The main thing, the NHS says, is to keep your skin cool so you stop sweating and irritating the rash. On Phi Phi that means:
- Get somewhere cool: air-conditioned rooms, cafés and the 7-Eleven are the quickest relief. A fan helps if you don’t have air conditioning.
- Wear loose cotton clothing and change out of damp swimwear or sweaty clothes as soon as you can.
- Take cool showers, and pat your skin dry rather than rubbing it.
- Use light bedding, or just a sheet, at night.
- Drink plenty of fluids, because the heat that causes the rash also dehydrates you.
- Calm the itch with something cold, like a damp cloth or a wrapped ice pack, for up to 20 minutes.
- Tap or pat the itchy area instead of scratching, which can break the skin and let infection in.
- Skip perfumed shower gels, lotions and heavy creams on the rash.
What to buy: pharmacies, 7-Eleven and prickly heat powder
If the itch is bothering you, speak to a pharmacist. In the UK the NHS says a pharmacist might suggest a soothing lotion, an antihistamine or a mild steroid cream, and pharmacists in Thailand can advise in the same way. Tell them about any other medicines you take, any allergies and whether the rash is on a child, because some treatments are not suitable for young children.
You will also see prickly heat powder for sale all over Thailand, including in 7-Eleven. It is a cooling talc-style powder that many Thai people use in the hot season, often with a menthol feel. Some travellers find it soothing on unbroken skin. Avoid using it on broken, weeping or scratched skin, keep it away from babies’ faces, and stop if it stings or makes things worse.
We don’t give medication advice online. If you’re not sure what to use, the pharmacist is the right person to ask.
When a rash needs a doctor, not a cream
See a doctor if the rash doesn’t improve after a few days, if the skin becomes hot, swollen, painful or weeps pus (signs of infection), or if a baby has a rash and you’re worried. A rash with a fever in Thailand always needs a doctor, because it can be a sign of an infection such as dengue. Call 1669 (Thailand emergency medical services) straight away for swelling of the lips, mouth or throat, trouble breathing, a rash that spreads very fast with feeling very unwell, confusion, or hot dry skin with collapse, which can be heatstroke. Our guide to medical help on Koh Phi Phi lists where to go.
How to prevent prickly heat on holiday
Heat rash is much easier to prevent than to get rid of. A few habits help:
- Choose a room with air conditioning or a good fan if you’re prone to it, especially in the hottest months.
- Avoid the strongest heat between late morning and mid-afternoon, and do active things like the viewpoint hike early or late.
- Change out of wet swimwear after swimming instead of sitting in it all afternoon.
- Pack loose, breathable clothing rather than tight synthetic tops and leggings.
- Use a light sunscreen rather than a very thick, greasy one, and wash it off in the evening.
- Keep babies and toddlers cool: they get heat rash easily because they can’t control their temperature as well as adults.
Heat rash or heat exhaustion?
Heat rash is a skin problem: annoying, but the person feels well. If you or a friend also feel dizzy, sick, headachy, very tired or very thirsty after time in the heat, that’s heat exhaustion, and it needs cooling down and fluids straight away. Read our guide to heat exhaustion in Thailand to know the warning signs, and when it becomes an emergency.
An IV drip doesn’t treat heat rash. If the heat has also left you dehydrated and drained, drinking water and oral rehydration salts is the first step, and our nurses can advise on WhatsApp if you’re struggling to catch up.
Heat rash FAQ
Heat rash in Thailand: your questions
How long does heat rash last?
It usually gets better on its own within a few days once your skin is kept cool and dry. If it hasn’t improved after a few days, see a doctor.
Can I swim with heat rash?
Usually yes, and a cool swim can feel good. Rinse off afterwards, pat dry and change out of wet swimwear quickly. Don’t swim if the skin is broken or looks infected.
Is prickly heat powder safe?
Many people find it soothing on unbroken skin. Don’t use it on broken or weeping skin, keep it away from babies’ faces, and stop if it irritates. Ask a pharmacist if you’re unsure.
Is heat rash contagious?
No. It comes from blocked sweat ducts and can’t be passed on to other people.
Why do I get heat rash in Thailand but not at home?
Heat and humidity together. In humid air sweat doesn’t evaporate well, so it stays on and in the skin. Most people get used to the climate after a while, but the first week is often the worst.
Keep reading
Looking after your skin in the tropics
See our guides to sunburn treatment in Thailand and heat exhaustion in Thailand, or read about mosquito and sand fly bites if your spots look more like bites.
Sources: NHS: Heat rash (prickly heat) · NHS: Heat exhaustion and heatstroke · WHO: Dengue and severe dengue. Last updated October 2026.
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