Body Concerns
Heat Rash
Heat rash, also called prickly heat, is an itchy or prickly rash of tiny bumps that appears when sweat gets trapped in the skin. Its medical name is miliaria. It is common in hot, humid weather and in babies, and it usually clears on its own once the skin cools down.
- Heat rash happens when sweat ducts get blocked and sweat leaks into the skin, causing tiny itchy or prickly bumps.
- Cooling the skin and avoiding sweat-trapping clothing and heavy creams is the main treatment, and most cases clear within days.
- Pus-filled spots, a rash that keeps spreading, or signs of heat exhaustion need medical attention.
Overview
What is heat rash?
Sweat travels from glands deep in the skin to the surface through tiny ducts. In heat rash, these ducts become blocked, so sweat leaks into the surrounding skin and causes irritation and small bumps. Doctors group miliaria by how deep the blockage is, which explains why heat rash can look so different from person to person.
It is very common. DermNet and StatPearls report that the most common type affects up to 30% of adults who move to, or are suddenly exposed to, hot and humid conditions. Newborns get it easily because their sweat ducts are still immature, and the most superficial type affects up to about 9% of newborns.
Heat rash is uncomfortable but usually harmless. NHS guidance says it tends to clear on its own within a few days, and DermNet notes most cases settle within a day or two of moving to a cooler place.
Common signs and patterns
What heat rash can look or feel like
These features give context but do not confirm a diagnosis on their own.
Tiny clear blisters
Miliaria crystallina: very small, clear blisters like beads of sweat that break easily and usually do not itch or hurt. Common in newborns.
Itchy, prickly red bumps
Miliaria rubra, or prickly heat: small bumps about 2 to 4 mm across with an intense itch or prickle. It is the most common type.
Bumps with pus
Miliaria pustulosa: prickly heat bumps that fill with pus. Infection can also cause pus-filled spots, so these are worth showing to a clinician.
Where it appears
Adults: upper back, chest, neck and skin folds where clothing rubs. Babies: neck, shoulders, chest, armpits and groin. On brown and black skin it can look grey or white rather than red.
Causes and contributors
Heavy sweating in hot, humid conditions is the main trigger, especially when skin cannot breathe.
Anything that makes you sweat a lot and stops sweat evaporating can set it off: hot, humid weather, hard exercise, fever, tight or synthetic clothing, and long periods lying on waterproof or non-breathable bedding, for example during illness. Babies who are overdressed or overwrapped are at higher risk.
Heavy creams and ointments that block sweat ducts can make it more likely, which is why dermatology sources advise avoiding them. Some medicines that increase sweating can also contribute; do not stop a prescribed medicine without talking to your doctor.
What it may be confused with
Similar-looking concerns need different decisions
Small bumps on hot, sweaty skin are not always heat rash, and some need different treatment.
Folliculitis
Red or pus-filled bumps centered on hair follicles, often after shaving or friction, caused by inflamed follicles rather than blocked sweat ducts.
Fungal acne
Itchy, same-sized bumps on the chest and back that are also linked to heat and sweat, but are driven by skin yeast and need antifungal treatment.
Chest acne
Spots of mixed sizes with blackheads or whiteheads, rather than uniform tiny bumps.
Contact dermatitis
An itchy rash where a product, fabric or plant touched the skin, which can appear in any weather.
Bottom line
Treat the heat, not just the rash.
Because heat rash comes from trapped sweat, the fix is to stop sweating so much and let the skin breathe: cooler rooms, loose cotton clothes, lighter bedding, cool showers and plenty of fluids. Most rashes then clear within a few days without other treatment.
Soothing products such as calamine lotion can ease itch while it settles. A rash that lasts more than a few days, keeps returning, shows pus or comes with feeling unwell deserves a clinician’s look, both to confirm it is heat rash and to check for infection.
Evidence-supported options
Choose the option that matches how severe it is
This is general education, not a personal treatment plan. Product strengths, permitted uses and prescription status vary by country.
Cool the skin down
Move to shade, air conditioning or a fan, take cool baths or showers, and wear loose cotton clothing. This removes the cause and is the main treatment.
Limit: It works only if the heat and sweating stop; returning to the same conditions often brings the rash back.
Soothe the itch
A cold compress for up to 20 minutes, patting instead of scratching, and calamine lotion can ease the prickle. A pharmacist may suggest an antihistamine tablet.
Limit: These ease symptoms but do not clear the blocked ducts.
Mild anti-inflammatory cream
For an inflamed, itchy rash that is not settling, a pharmacist or doctor may suggest a mild steroid cream such as hydrocortisone for a short time.
Limit: NHS advice is not to use hydrocortisone on children under 10 without a doctor’s advice. An infected rash needs different treatment.
Stay cool before it starts
Loose, moisture-wicking clothes, a cool, ventilated bedroom, limiting hard activity in the heat and not overdressing babies all reduce sweating.
Limit: Recurrence is common in hot climates even with good habits.
Supportive skincare
A simple plan while heat rash settles
Keep skin cool, dry and lightly covered; less is more on the rash itself.
Daily care
- Cool rinseShower in cool water and pat skin dry gently rather than rubbing.
- Light layers onlySkip heavy creams and ointments on the rash. If you need sunscreen there, choose a light lotion or gel; see the summer skincare routine.
- Calm the itchUse a cold compress or calamine lotion when it prickles, and avoid perfumed shower gels and creams.
Prevention
- Dress for airflowChoose loose cotton or moisture-wicking fabrics and change out of sweaty clothes quickly.
- Cool sleepUse lightweight bedding and keep the bedroom cool and ventilated.
- Pace the heatDrink plenty of fluids and limit hard exercise in the hottest part of the day.
Common mistakes
What can make heat rash harder to manage
- Covering the rash with thick, greasy creams or ointments, which trap more sweat.
- Scratching, which irritates the skin and raises the risk of infection.
- Using perfumed shower gels or lotions on the rash.
- Staying in damp, sweaty or tight synthetic clothing.
- Overdressing or overwrapping a baby in warm weather.
When professional help makes sense
Seek assessment when heat rash does not settle or you feel unwell
- The rash has not improved after a few days, or it keeps getting worse.
- Bumps fill with pus or become increasingly red, sore or swollen, which can mean a bacterial infection.
- Your baby has a rash and you are worried; if a baby or child seems unwell, get medical advice promptly.
- Dizziness, headache, nausea, cramps or feeling very hot and unwell suggest heat exhaustion; move somewhere cool, drink water and get help if not better within 30 minutes.
- Hot skin that has stopped sweating, confusion, fast breathing, a seizure or collapse can mean heatstroke and is an emergency.
Related reading
Continue with the next useful question
Editorial record
What this page knows, and what remains uncertain
Evidence summary
This page relies on the NHS, DermNet, StatPearls and Mayo Clinic. They agree that heat rash comes from blocked sweat ducts and that cooling the skin is the main treatment.
Important limitations
Most advice on heat rash is based on clinical experience rather than trials, and the rarer deep form has very limited treatment evidence.
Financial transparency
No paid product placement or affiliate ranking is included on this foundation page.
Recommendation logic
Options run from cooling and soothing to a short course of mild cream, with prevention for people who get it often.
Editorial Record
- Editorial status
- reviewed
- Medical reviewer
- Dr. Abdurrahman Efem
- Practical reviewer
- Merve Akkaya
- Last reviewed
- November 13, 2026
Frequently asked questions
Short answers to common questions
How long does heat rash last?
It usually clears within a few days once the skin is kept cool. DermNet notes most cases settle within a day or two of moving to a cooler place.
What does heat rash look like on dark skin?
On brown and black skin it can be harder to see and may look grey or white rather than red. Mayo Clinic notes that brown and black skin can be left with lighter or darker spots that usually fade within weeks or months.
Is heat rash contagious?
No. It comes from blocked sweat ducts, not an infection, so it cannot spread to other people.
What is the fastest way to get rid of heat rash?
Cool down and stop sweating: move to a cooler place, wear loose cotton clothing, take a cool shower and use a cold compress. Calamine lotion can ease the itch meanwhile.
Should I put moisturizer on heat rash?
Avoid thick creams and ointments on the rash because they can trap sweat. If skin becomes dry after calamine, a light moisturizer is reasonable.
Can adults get heat rash?
Yes. It is common in adults in hot, humid conditions, during hard exercise and when clothing traps sweat, usually on the upper body and in skin folds.
Sources reviewed
Guidance behind this page
- NHS: Heat rash (prickly heat).
- DermNet: Miliaria (Oakley A, Eshraghi A, revised 2020).
- StatPearls: Miliaria. StatPearls Publishing, updated 2024.
- Mayo Clinic: Heat rash, symptoms and causes.
- NHS: Heat exhaustion and heatstroke.
Sources support general editorial guidance. They do not replace regional product labels, prescribing information or personal medical assessment.