What is heat rash?

Heat rash is a common skin condition caused by heat. It's also called prickly heat, sweat rash or miliaria.

Heat rash can look different depending on the type. You may notice:

• tiny clear blisters that break easily
• small red spots or bumps that may feel itchy
• deeper red or white lumps that feel prickly but are usually not itchy

Heat rash appears in places where sweat collects, such as:

• under your breasts or armpits
• neck and upper chest
• skin folds
• groin
• around your waist

In babies, heat rash may also appear on their face and in the nappy area.

What causes heat rash?

Heat rash happens when sweat ducts (tiny tubes that carry sweat to the skin surface) get blocked. This stops sweat from coming out and makes it build up under the skin.

You have a higher chance of developing heat rash when you:

• are in hot and humid weather, such as during summer
• wear tight or heavy clothes that trap heat and moisture
• have a fever
• get sunburnt
• have too much sodium and not enough water in your blood (hypernatremia)

Babies often get heat rash because their sweat glands are not fully developed. Your baby has a higher chance of getting heat rash if they are bundled (swaddled) or wrapped in too many layers.

When should I see my doctor?

See your doctor if the rash:

• does not get better after a few days in a cooler place
• covers a large area
• looks different from usual heat rash
• keeps coming back

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When to seek urgent care?

Seek urgent care if you or your baby has signs of infection, such as:

• lumps filled with pus
• redness around the rash
• a high temperature (fever)

Also seek urgent care if you or your baby show signs of heat stroke. Read more on heat-related illness in babies.

How is heat rash diagnosed?

Your doctor will diagnose heat rash by looking at your rash.

Sometimes, a sample of your skin (skin biopsy) may be needed to check for other conditions.

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How is heat rash treated?

Heat rash usually gets better when your skin is kept cool and dry. Treatment depends on how severe the rash is and whether you have any complications.

Self-care at home

Often, heat rash gets better on its own with these simple steps:

• stay in a cool, well-ventilated place
• have cool baths — good personal hygiene helps remove sweat and bacteria
• wear loose cotton clothing and avoid tight or synthetic fabrics that trap heat and sweat
• use cornstarch or absorbent powders to keep your skin dry
• apply a gentle moisturiser if your skin is dry or itchy

Medicines for heat rash

Sometimes you may need to apply a product to your skin to help with symptoms, especially if the rash is itchy or painful. These may contain prescription medicines or might be available over the counter, for example:

• lotions or creams (such as calamine lotion) to cool and soothe itchy skin
• antibacterial creams, ointments or washes if there is a chance of infection
• topical corticosteroid creams or ointments (prescribed by a doctor) for severe rashes that don't improve with other treatments

Ask your doctor or pharmacist about medicines or other creams that may help you.

How can I help my baby with heat rash?

Here are some tips to help your baby:

• move them to a cooler room or shaded area
• change sweaty clothes and wet nappies regularly
• remove extra layers of clothing or blankets and dress them in loose, light cotton clothes
• keep their skin clean and dry
• apply soothing lotion, such as calamine, followed by a gentle moisturiser if their skin is irritated

What are the complications of heat rash?

Your heat rash can sometimes become infected and turn into pus-filled lumps (abscesses).

If a large area of your body is covered by heat rash, you may develop heatstroke.

Can heat rash be prevented?

To prevent heat rash from developing or getting worse, there are things you can do:

• Keep cool to avoid sweating.
• Try to avoid heat and humidity.
• Stay in air conditioning, near a fan or in a well-ventilated space.
• Wear loose cotton clothing to stop overheating.
• Avoid fabrics that irritate your skin.

Resources and support

• DermNet has information about heat rash.
• NSW Health has information on heat-related illnesses, including heat rash.
• The Royal Women's Hospital has information on heatwave precautions for babies and young children.
• Australian Red Cross has information on the risks and potential impacts of extreme heat in your area.
• Queensland Government has information on hot weather, health and safety.
• The Northern Territory Government has a video on heat safety.
• NSW Government has translated resources on protecting yourself from the heat.

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available to speak with you 24 hours a day, 7 days a week.