Heat rash in babies: what it looks like and what to do

Why do babies get heat rash?

Heat rash is also called prickly heat or miliaria. Sweat ducts, the tiny channels that carry sweat to the skin's surface, become blocked. Newborns have immature sweat ducts, and babies cannot control their temperature as well as older children and adults. Hot, humid surroundings make the problem more likely, but excessive clothing can also trap heat.13

What does heat rash look like on a baby?

The common prickly form has small raised spots, usually 2 to 4 millimetres across, with itching and sometimes mild swelling. Some spots contain fluid. The rash looks red on white skin; on brown or black skin, spots can look grey or white and be harder to see. Colour alone is not a useful way to rule it out.3

Another form, called miliaria crystallina, produces clear blisters about 1 to 2 millimetres across. These sit near the skin's surface, resemble beads of sweat and break easily, sometimes leaving fine flakes. Unlike the prickly form, this type has no surrounding inflammation. It commonly appears on the head, neck and upper body.1

In babies, heat rash often develops on the neck, armpits, elbow creases and groin. It can also affect the body and other skin folds. Although heat rash can spread across the skin, it is not contagious. A baby with uncomplicated heat rash should otherwise act normally, without fever or signs of illness.23

How to cool and soothe your baby's skin

1. 1Move your baby out of the heat into a cooler area. A fan can help with cooling.
2. 2Remove extra clothing. Choose loose, breathable cotton rather than tight or heavy clothes.
3. 3Gently wipe the skin with a cool, damp washcloth to remove sweat and body oils.
4. 4Give your baby a lukewarm bath if needed, then gently dry away excess moisture.
5. 5Keep the room cool and ventilated, and use lightweight bedding rather than extra blankets.

For a prickly or itchy patch, use a cool damp cloth. A cold compress can be applied for up to 20 minutes; wrap an ice pack in a towel rather than putting it directly on skin. Pat the area instead of scratching, and avoid perfumed wash products and creams.3

Does your baby need a cream?

Start with cooling rather than applying lotions, oils, creams or ointments. These can further block sweat ducts and trap moisture, making heat rash worse. An uncomplicated rash usually clears without a skin treatment.2

If discomfort continues, ask a pharmacist which treatment is suitable for your baby's age. Calamine can relieve discomfort, but it also dries the skin. Do not use hydrocortisone on a baby without a doctor's advice: children under 10 need medical advice before using it. Antihistamine tablets listed as general heat rash treatments are not a reason to give them to a baby.13

How long does baby heat rash last?

Most cases resolve within a day or two after moving to a cooler environment, although clearing can take a few days. Typical heat rash leaves no permanent skin damage. If the rash is not improving after a few days, or is getting worse, contact your baby's doctor rather than continuing to treat it as heat rash.12

How to help prevent another episode

Loose cotton clothing allows air to circulate and sweat to evaporate, giving the wardrobe a job beyond looking adorable. Avoid overdressing your baby or using fabrics too heavy for the weather. Change wet clothing and keep sleeping surroundings cool.12

Lightweight bedding helps keep skin cool, so the nursery does not need to audition for a tropical resort. Keep the same cooling approach at night: too many blankets can contribute to heat rash just as extra clothing can during the day.23

When should you contact a doctor?

Small bumps do not identify the cause of a rash on their own. Irritation, allergies and infections can also cause rashes, and treatment depends on the cause. Contact a doctor if you are unsure what the rash is, it is severe or persistent, or your baby has other symptoms. You can also seek advice simply because you are worried.4

Seek medical care if your baby has a fever, seems sick, or develops signs of infection. These include increasing pain, swelling, redness or warmth around the rash, scabs, and swollen glands in the neck, armpits or groin. Tiny clear blisters can occur with heat rash itself; blisters with worsening skin changes or illness need assessment.12

Use a digital thermometer to check for fever. Get urgent medical advice for a baby under 3 months with a temperature of 38 C or higher, or a baby aged 3 months or older with a temperature of 39 C or higher. Do not wait for those temperatures if your baby seems unwell: serious illness can happen without fever.5

Which symptoms need emergency help?

Call your local emergency number if your baby is unwell with a rash and has any of these signs:

• Difficulty breathing, grunting, very fast breathing or the tummy pulling in beneath the ribs.
• Unusual agitation or not responding normally.
• Pale, blue, grey or blotchy skin, lips or tongue.
• Sudden swelling of the lips, mouth, throat or tongue, or difficulty swallowing.
• A stiff neck or sensitivity to light.
• Spots that resemble bruises or bleeding beneath the skin and do not fade when pressed with a glass.

Heat rash is skin irritation from sweating; heat exhaustion and heat stroke affect the body's ability to cope with heat. Young children are particularly vulnerable to heat illness. Rapid breathing and heavy sweating can accompany heat exhaustion, while heat stroke is life threatening. A baby who seems ill after heat exposure needs medical assessment, not just treatment of the visible rash.6