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Medical Dermatology

Heat Rash (Miliaria)

Small, itchy, prickly bumps that flare in the heat are one of the most quintessentially tropical skin complaints. Heat rash is harmless and usually settles quickly once the skin is kept cool and dry — but it is worth knowing how to tell it apart from other itchy rashes.

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At a glance

What it is
A rash caused by blocked sweat ducts trapping sweat under the skin — also called miliaria or prickly heat.
Who it affects
Anyone in hot, humid conditions, and especially babies, whose sweat glands are still immature.
Common sites
Upper back, chest, neck and skin folds in adults; neck, armpits and groin in babies.
Why it happens here
Singapore's constant heat and humidity mean sweat often cannot evaporate — the direct cause.
Treatment
Cool the skin and let it dry. Most heat rash settles within days without specific medication.
Understanding the condition

What causes heat rash?

Sweat normally travels along tiny ducts from the sweat glands to the skin surface, where it evaporates and cools you down. In heat rash, these sweat ducts become blocked, so sweat is trapped beneath the skin rather than reaching the surface. The trapped sweat leaks into the surrounding skin and produces the characteristic small, itchy or prickly bumps.

In Singapore's climate, the humidity rarely drops below 80%, which means sweat often has nowhere to evaporate to. This is exactly the situation that leads to heat rash — and why it is seen so frequently here, particularly in babies, whose sweat glands have not fully matured.

Not an allergy or an infection Heat rash is a plumbing problem, not an immune one — it is blocked sweat ducts, not a reaction to an allergen or a germ. It can occasionally become infected if the skin is broken by scratching, but in itself it is simply trapped sweat.
Recognising it

Where heat rash appears

It follows wherever sweat collects and cannot evaporate freely.

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In adults

  • Upper back, chest and neck
  • Skin folds where sweat collects
  • Areas covered by tight clothing
  • Worse after exertion or time in the heat
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In babies

  • Neck, armpits and groin
  • Where clothing or wraps trap heat
  • Common when over-dressed
  • Usually settles quickly once cooled
Can be mistaken for other rashes An itchy rash in the heat can resemble eczema, a fungal infection or an allergic reaction. Heat rash characteristically settles when the skin is kept cool and dry — if it does not, it is worth having the diagnosis confirmed.
Treatment

How heat rash is treated

The treatment follows directly from the cause: cool the skin and let it dry. Most heat rash settles within a few days once this is done, with no need for specific medication.

  • Move to a cooler or air-conditioned environment
  • Remove tight or damp clothing and let the skin breathe
  • Cool the skin with a lukewarm shower and pat it dry
  • Use light, soothing preparations for itch if needed
  • Avoid heavy, greasy creams, which can further block the sweat ducts

For babies, the mainstay is simply keeping them cool and avoiding over-dressing. If the skin has been scratched and looks infected, that may need specific treatment.

Everyday care

Preventing heat rash

Hard to avoid entirely in the tropics, but these measures make it much less likely.

Helpful

  • Wear loose, breathable, light cotton clothing
  • Stay cool and make use of air-conditioning and fans
  • Shower and dry off after sweating
  • Keep skin folds clean and dry
  • For babies, dress lightly and avoid over-wrapping

Unhelpful

  • Tight, synthetic clothing that traps sweat
  • Heavy, occlusive creams and ointments
  • Staying in damp, sweaty clothes
  • Over-dressing babies and young children
  • Scratching, which can break the skin and invite infection
Seeking help

When to see a doctor

Most heat rash needs no medical attention. Consider assessment if:

  • The rash is not improving with cooling measures
  • It is very itchy or widespread
  • The skin looks infected — increasingly red, painful or weeping
  • You are unsure whether it is heat rash or another condition
  • In a baby, the rash is extensive or the child is unwell or feverish
Dr Chen Qiping, Consultant Dermatologist, Chen Dermatology Singapore

Dr Chen Qiping

Consultant Dermatologist · MBBS, MRCP (UK), M.Sc, FAMS (Dermatology)

Dr Chen practises general adult and paediatric dermatology, including heat-related and other rashes, alongside surgical, laser and cosmetic dermatology. Consultations are available in English and Mandarin.

Full profile →
Common questions

Heat rash — frequently asked questions

What exactly is heat rash?
Heat rash, or miliaria, occurs when sweat ducts become blocked and sweat is trapped under the skin instead of reaching the surface. The trapped sweat causes small itchy bumps or blisters. It is directly related to heat, humidity and sweating, which is why it is so common in Singapore's climate and in babies, whose sweat glands are still immature.
Where does heat rash usually appear?
In adults it typically affects areas where sweat collects or clothing traps heat — the upper back, chest, neck and skin folds, and areas covered by tight clothing. In babies and young children it commonly appears on the neck, in the armpits and the groin. The distribution follows wherever sweat cannot evaporate freely.
How do I get rid of heat rash quickly?
The most important step is to cool the skin and let it dry. Moving to a cooler or air-conditioned environment, removing tight or damp clothing, and allowing the skin to breathe usually settles it within a few days. Loose, breathable clothing and avoiding further overheating prevent it recurring. Most heat rash resolves on its own once the skin is kept cool and dry, without any specific medication.
Is heat rash the same as an allergy or an infection?
No. Heat rash is caused by blocked sweat ducts, not by an allergen or an infection, although it can occasionally become secondarily infected if the skin is broken by scratching. It can, however, be mistaken for other itchy rashes such as eczema or a fungal infection, which is one reason a rash that does not settle with cooling is worth having assessed.
Can heat rash be prevented?
Largely, yes, by reducing the conditions that cause it. Staying cool, wearing loose breathable clothing, avoiding prolonged overheating and sweating, and keeping the skin dry all help. For babies, avoiding over-dressing and keeping them cool is the mainstay. In a hot, humid climate it is not always fully avoidable, but these measures make it much less likely and less severe.
When should I see a doctor about heat rash?
Most heat rash settles on its own and does not need medical attention. Consider assessment if the rash is not improving with cooling measures, if it is very itchy or widespread, if the skin looks infected — increasingly red, painful, or weeping — or if you are unsure whether it is heat rash or another condition. In babies, seek advice if the rash is extensive or the child is unwell or feverish.

References

  1. DermNet. Miliaria. dermnetnz.org
  2. Mayo Clinic. Heat rash — Symptoms and causes. mayoclinic.org
  3. American Academy of Dermatology. Heat rash. aad.org

Page last reviewed: 28 July 2026.

Important — This page is general information about a skin condition and is not medical advice. It cannot take the place of an individual consultation, examination and diagnosis. Treatment options, their suitability and their possible side effects should be discussed with a qualified doctor who has assessed your skin. Individual results vary. If you have concerns about your skin, please arrange a consultation.

Have an itchy rash that flares in the heat?

Arrange a consultation with Dr Chen Qiping at our Collyer Quay clinic — two minutes' walk from Raffles Place MRT. Consultations available in English and Mandarin.

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