Heat Rash (Prickly Heat): Pictures, Causes & Treatment
Heat rash — miliaria, also called prickly heat or sweat rash — develops when sweat ducts become blocked and sweat leaks into the surrounding skin. It is common in hot, humid weather, under occlusive clothing, and in babies whose sweat ducts are still immature.
Medically reviewed by Dr. Celina Kazumi Iwasa, MD · Last reviewed 2026-08-23
Quick answer
Heat rash is a prickly, itchy rash of tiny clear blisters or small red bumps caused by blocked sweat ducts. It appears in hot, humid conditions on the neck, chest, back, skin folds and areas covered by tight clothing. Most cases clear within a few days simply by cooling the skin, wearing loose cotton, and keeping the area dry. Bumps that become pustular, painful or feverish suggest infection and need medical review.
What heat rash looks like
The appearance depends on how deep the sweat duct is blocked. Miliaria crystallina is superficial: tiny clear fragile blisters with no redness or itch. Miliaria rubra — classic prickly heat — sits deeper and produces small inflamed bumps with a stinging, prickling sensation. Miliaria profunda causes firmer, flesh-coloured bumps after repeated episodes.
Common locations
- Neck, upper chest and back
- Under the breasts and in the groin
- Armpits and elbow creases
- Waistband, nappy area and under straps
- Anywhere covered by tight or non-breathable clothing
Typical signs
- Crops of tiny bumps or clear blisters
- Prickling, stinging or burning rather than pure itch
- Rash confined to hot, covered or occluded areas
- Rapid improvement once the skin cools down
- Reduced sweating in the affected area in deeper forms
On brown and Black skin
On brown and Black skin the bumps may look skin-coloured, grey or slightly darker rather than red, so the prickling sensation and the location are more reliable clues than colour.
Causes and triggers
Anything that blocks sweat ducts or increases sweating without letting it evaporate can cause miliaria. Skin surface bacteria contribute to duct plugging, which is why it can recur in the same areas.
| Trigger | Why it matters |
|---|---|
| Hot, humid climates | Sweat cannot evaporate, so ducts swell and block — a common holiday and summer complaint. |
| Tight or synthetic clothing | Occlusion traps sweat directly against the skin surface. |
| Fever and bed rest | Sustained sweating with the skin pressed against bedding blocks ducts on the back. |
| Babies and infants | Immature sweat ducts, plus swaddling and warm rooms, make miliaria very common in the first weeks of life. |
| Heavy exercise and manual work | High sweat output under PPE, uniforms or backpacks. |
| Thick creams and ointments | Occlusive products and some adhesive dressings physically plug duct openings. |
Conditions that look similar
Heat rash is often confused with other bumpy rashes. The trigger, sensation and response to cooling usually settle it.
| Condition | How to tell it apart |
|---|---|
| Folliculitis | Pustules centred on hair follicles, often tender; does not clear within hours of cooling. |
| Hives | Larger raised welts that move around and fade within 24 hours, not fixed pinpoint bumps. |
| Fungal intertrigo | Moist, well-defined red patches in folds with a scaly edge and satellite spots; needs antifungal treatment. |
| Contact dermatitis | Follows the shape of a product or garment and continues even when cool. |
| Viral rash | Spreads over the whole body with fever and other symptoms rather than sitting in hot, covered areas. |
Treatment options
Heat rash is self-limiting: cool the skin and stop the sweating cycle and it resolves, usually within two to three days. Treatment is mostly environmental rather than medicated.
Cool the skin
Move somewhere air-conditioned or shaded, take a cool shower and let skin air-dry rather than rubbing. A fan and cool damp compresses give quick relief from the prickling.
Change what you wear
Loose, lightweight cotton or moisture-wicking fabric; remove tight straps, waistbands and synthetic layers. For babies, reduce layers and keep the room cool.
Keep the area dry
Dry skin folds thoroughly after washing. Avoid thick occlusive creams, oils and heavy powders on affected areas until the rash has cleared.
Soothe symptoms
Calamine or a light non-occlusive moisturiser can ease prickling. A short course of a mild topical steroid may be used for persistent miliaria rubra on medical advice.
Prevent recurrence
Acclimatise gradually to hot climates, shower promptly after exercise, and choose breathable work clothing. People who repeatedly get heat rash under PPE should schedule cool-down breaks.
When to see a doctor
Most heat rash needs no medical care. Get advice if it does not improve within a few days of cooling, becomes painful or pustular, or affects a young baby who seems unwell.
Red flags
- Pus-filled, painful or spreading bumps (possible infection)
- Fever, chills or feeling generally unwell
- Extensive rash with dizziness, nausea or a lack of sweating (possible heat illness — urgent)
- A baby who is unsettled, feverish or feeding poorly with a rash
- Rash persisting more than a week despite cooling measures
Frequently asked questions
How long does heat rash last?
Simple heat rash improves within hours of cooling the skin and usually clears in two to three days. Deeper miliaria rubra can take up to a week. If it persists beyond a week despite staying cool and wearing loose clothing, the diagnosis may be something else.
How do you get rid of heat rash fast?
Get out of the heat, take a cool shower, let the skin air-dry, and switch to loose cotton clothing. Use a fan or cool compresses on the affected area, and avoid thick creams, oils and powders that block sweat ducts further. Calamine can ease prickling while the rash settles.
What is the difference between heat rash and hives?
Heat rash produces fixed crops of tiny bumps or blisters in hot, covered areas and prickles or stings. Hives are larger raised welts that appear anywhere, itch intensely, migrate around the body and individually fade within 24 hours.
Can adults get heat rash?
Yes. Adults commonly develop it during heatwaves, on tropical holidays, during intense exercise, under uniforms or PPE, or while feverish and bedbound. Babies get it more often only because their sweat ducts are still developing.
Should I put cream on heat rash?
Avoid thick, greasy creams and ointments — they block the sweat ducts that caused the problem. Cool water, calamine or a light lotion are better. A mild topical steroid is occasionally prescribed for stubborn, itchy miliaria rubra.
Is heat rash contagious?
No. Heat rash is a physical blockage of sweat ducts, not an infection, and cannot be passed to anyone else. If the bumps become pustular, a secondary bacterial infection may have developed and should be assessed.
Not sure if it is heat rash?
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Check your skin nowRelated guides
- Heat rash (miliaria): full clinical A–Z entry
- Hives (urticaria): how to tell them apart
- Folliculitis
- Sun safety hub
- Skin rash types: identify a rash by pattern
This page is for general information and does not replace a medical consultation. If you are worried about a skin change, see a qualified clinician.