Baby Heat Rash: What It Looks Like and How to Dress to Prevent It

It's a warm afternoon, and you lift your newborn out of her nap to find a cluster of tiny red spots across her neck folds and chest. Heat rash in babies, also called prickly heat or miliaria, is especially common in newborns, and it usually improves once she's kept cool and dry.

Where the spots sit, and whether they ease as she cools off, will tell you most of what you need to know. After that, prevention comes down to what she's wearing: loose, light cotton, fewer layers and nothing tight where sweat gathers.

If the spots don't fade when you press on them, or your baby seems floppy and very unwell, get medical help straight away. The glass test further down shows you how to check.

What Baby Heat Rash Looks Like

Heat rash can take a few forms, and healthdirect describes three of them:

• Tiny, clear blisters filled with fluid that pop easily (miliaria crystallina)

• Small red spots or bumps that can feel itchy or prickly (miliaria rubra)

• Deeper, firmer lumps with a prickly feel (miliaria profunda)

The colour changes with your baby's skin tone. According to Raising Children Network, the spots look red on lighter skin and can look brown, purple or grey on darker skin. Running your fingertips over the area helps, because the tiny raised bumps are often easier to feel than to see.

Heat rash turns up wherever sweat collects. On babies, the usual spots are:

• The neck folds and under the chin

• The chest and upper back

• The armpits, elbow creases and other skin folds

• The groin and nappy area

• The face and forehead

You'll also find it where fabric holds warmth against her skin. Check under a hat band, along the elastic of a bodysuit, on the back of her head after a nap, and across her back and bottom after a long stretch in the car seat or pram.

The spots usually sit in clusters where she's been warmest. Some babies don't seem bothered at all, while others fuss, rub at the area or sleep badly. Older babies and toddlers may scratch.

Why Babies Get Heat Rash So Easily

Sweat normally travels up a tiny duct and dries off the surface of the skin. When that duct is blocked, the sweat gets stuck underneath. As healthdirect and Raising Children Network explain, that trapped sweat inflames the skin around it, which is what raises the bumps.

Newborns are especially prone because their sweat glands are still developing, which is why heat rash shows up so often in the first weeks of life. A young baby also can't wriggle out of a layer, move into the shade or tell you she's too warm, so noticing falls to you.

The most common triggers include:

• Too many layers, or being bundled or wrapped in heavy fabric

• Tight or heavy clothes that hold in heat and moisture

• Hot, humid weather, like a Queensland or Top End summer

• Synthetic fabrics such as polyester, fleece or nylon blends

• Thick, greasy creams and ointments

• Fever

Long stretches pressed against padding in a car seat, carrier or pram can have the same effect, since sweat on her back has nowhere to go. Because overdressing and fever are both triggers, heat rash can appear in the cooler months too.

Toddlers get it as well, more often from sweating through active play. The same cooling steps help at any age.

Heat Rash or Something Else?

A few other common baby rashes can look similar at first. With heat rash, the clues are its location and behaviour: it gathers in sweaty areas and under clothing, it improves once your baby is cool and dry, and she's otherwise well.

Here's how the usual look-alikes compare:

Heat rash can also appear in the nappy area, so it's possible to see both there at once. If you're unsure what you're looking at, your GP can check.

The Glass Test

Press the side of a clear drinking glass gently but firmly against the spots. Heat rash usually fades under the pressure.

According to NSW Health, a rash that stays visible through the glass, such as red or purple pinprick spots or bruise-like patches, can be a sign of meningococcal disease. Call 000 or go to your nearest emergency department straight away, especially if your baby has a fever or seems unwell.

This rash can show up late in the illness. If your baby seems very unwell, get help without waiting for spots to appear.

How to Soothe Heat Rash at Home

Most heat rash settles without treatment once your baby stays cool and dry. Raising Children Network says it should clear in two to three days, though it can take longer.

Advice from healthdirect, Raising Children Network and NSW Health covers these steps:

• Move her somewhere cooler, like a shaded or air-conditioned room. A fan helps the air circulate, but keep it out of reach and aimed away from her.

• Take off extra layers and blankets. If the room is comfortable, a nappy on its own is fine for a while.

• Give her a lukewarm bath with a soap-free wash. Avoid cold water.

• Pat her dry gently, with extra care in the skin folds.

• Change damp clothes and wet nappies as soon as you notice them.

• Dress her again in one loose, light cotton layer.

• Cool a hot patch with a damp, soft cloth.

1) Creams, Lotions and Powders

Raising Children Network lists greasy ointments as a cause of heat rash. Thick creams hold warmth against the skin and can block sweat ducts further. Zinc nappy creams are thick barrier creams made for nappy rash, so ask your pharmacist before putting one on heat rash.

Baby powder won't prevent heat rash or help it clear, according to MedlinePlus. If her skin looks irritated, ask your pharmacist what's suitable for a baby her age.

Keep her nails short. If she's scratching a lot, talk to your GP about whether a cream would help, since less scratching lowers the chance of infection.

2) Feeds in Hot Weather

Babies under six months may want extra breastfeeds or formula feeds when it's hot. Both NSW Health and Red Nose recommend extra feeds in the heat. Breastmilk gives breastfed babies this age all the fluid they need, so they don’t need extra water.

When to See a GP

Raising Children Network and healthdirect recommend booking in with your GP if:

• The rash hasn't improved after three days, or isn't settling somewhere cooler

• Blisters fill with yellow or white pus

• Redness spreads around the rash

• Your baby has a fever, seems unwell or isn't feeding well

• The rash covers a large area or keeps coming back

NSW Health lists fewer wet nappies, darker urine and a dry mouth or skin as early signs your baby needs more fluid. Offer extra feeds and check in with your GP.

Get urgent help straight away if:

• Your baby is under three months old and has a temperature of 38°C or more. healthdirect advises going to the nearest emergency department.

• She's limp or floppy, drowsy, pale, cold to touch or refusing feeds, or her eyes look sunken. NSW Health advises calling 000.

• The rash doesn't fade under a glass. Call 000 or go to emergency.

How to Dress Your Baby to Prevent Heat Rash

Heat rash starts when sweat can't escape, so on warm days you want it drying off her skin as fast as it appears. You can help most by choosing light fabrics, leaving room in the fit and keeping layers to a minimum.

1) Choose Breathable Cotton

For babies with heat rash, healthdirect recommends loose, light cotton. Cotton soaks up sweat and lets air reach her skin, so moisture doesn't sit against it. That's why it's the everyday fabric we reach for in summer.

On hot days, leave polyester, fleece, nylon blends and heavy plush in the drawer. healthdirect advises against synthetic fabrics because they trap heat and hold sweat against the skin.

Lighter cotton weaves like waffle, gauze and muslin make easy picks for the hottest part of the day. Our summer bodysuits are made for these months, and the cotton waffle Summer Bodysuit & Sun Hat comes with a matching hat for outdoors. Add light pants if the afternoon cools.

Organic cotton breathes the same way and feels soft on new skin. Keep in mind that no fabric can promise to prevent a rash.

Our knits suit cool mornings and air-conditioned rooms. A piece from our summer knitwear takes the chill off first thing, then comes off once she warms up.

2) Get the Fit Right

Look for clothes loose enough that air can move between fabric and skin, without so much spare fabric that it bunches in her folds. Tight elastic at the neck, leg holes or waistband holds in heat and moisture, and you'll often see heat rash start along those lines.

On hot days, sleeveless or short-sleeved bodysuits with open necklines keep fabric clear of her neck folds. If a bodysuit leaves red marks at the legs or neck, she may be ready for the next size. Our guide on when to size up baby clothes covers the other signs.

Save hats for sun protection outdoors. Red Nose recommends taking hats and bonnets off once you're inside, and it's a good habit in the car too. Check under the band for spots when you do.

3) Dress for the Temperature in the Room

Red Nose suggests dressing your baby the way you'd dress yourself for the room you're both in. On a hot day, that might mean one light cotton bodysuit or singlet, or a nappy on its own indoors.

To check whether she's comfortable, feel her tummy. Cool hands and feet are normal and don't mean she needs another layer. If her tummy feels hot or sweaty, take something off.

For outfit ideas through the warmer months, our guide on how to dress a newborn in summer walks through what to put on at different temperatures.

4) Swaddling and Sleep in Warm Weather

Being wrapped in too many layers is a common heat rash trigger. On hot nights, Red Nose recommends one lightweight cotton or muslin wrap with only a nappy and singlet underneath. It also advises against using a wrap and a sleeping bag together.

Our fringe swaddle blankets are made from double-layer cotton gauze, light enough to wrap with all year. The Fringe Swaddle Blanket in Sun is one example.

Red Nose advises stopping wrapping when she shows signs of rolling or reaches three months of age. If you use a sleeping bag instead, match its TOG rating to the room. Our guide on how to swaddle a baby safely walks through the technique step by step.

Red Nose links overheating to a higher risk of sudden unexpected death in infancy, or SUDI, so keep her head and face uncovered and leave hats and bonnets off for sleep.

5) Car Seats, Carriers and Prams

All three hold your baby against padding for long periods, so sweat on her back, bottom and head can't dry.

In the car, cool it down before she gets in, use window sunshades and keep her in one light layer. NSW Health warns never to cover a capsule with a rug or towel, and never to leave a baby alone in the car. When you arrive, check her back and neck for damp skin.

On hot days, skip carriers and slings where you can. WA Health's heatwave advice for parents notes that they restrict airflow and babies can overheat in them. If you need one, dress her lighter than usual and take regular breaks so her skin can dry.

For the pram, use the canopy for shade and take out the back panel if it has one, so air can move through. NSW Health warns that draping a dry wrap or blanket over the pram cuts airflow and can make it dangerously hot inside.

NSW Health also advises against letting babies sleep in the pram on hot days. On longer outings, pack a spare light bodysuit so you can swap her out of damp clothes.

6) Air the Skin Every Day

A little nappy-free time on a cotton blanket in a cool room lets her skin dry out completely. Raising Children Network recommends drying her skin folds well after every bath, and in hot weather it helps to do the same after feeds.

Swap sweaty clothes during the day as well as at bedtime. After skin-to-skin or a feed in a warm room, let her chest and neck air-dry for a minute before you dress her again.

Our babywear range includes sleeveless and short-sleeved cotton bodysuits, so a few extras in the drawer mean there's always a dry one ready.

What to Reach for on the Next Hot Day

When those tiny red spots appear, cool her down first: a shaded room, fewer layers, a lukewarm bath and a dry, loose cotton bodysuit. Most heat rash improves within a few days. See your GP if it hasn't, and call 000 for any rash that doesn't fade under a glass.

To stop it coming back, keep a few light cotton pieces in rotation, check her tummy when you're unsure how warm she is, and take hats and extra wraps off indoors.

Plenty of Mummas meet heat rash in bub's first summer, and a quick look at her neck folds after a warm nap will usually catch it early.