Heat Rash in Babies

When to get help

Call emergency services — 999 in the UK, 112 or 999 in Ireland and across the EU, 911 in the US and Canada, 000 in Australia, 111 in New Zealand — if your baby has a rash that does not fade when you press a clear glass against it, or if they are drowsy and hard to wake, floppy, breathing fast, vomiting repeatedly, or have hot dry skin and are not sweating. The last group are heatstroke signs, and the NHS treats heatstroke as a medical emergency.

Seek same-day advice — NHS 111 in the UK, GP or out-of-hours in Ireland, paediatrician in the US or Canada, healthdirect on 1800 022 222 in Australia, Healthline on 0800 611 116 in New Zealand — if the rash is not improving after a few days of cooling measures, if the spots become pus-filled, if the skin becomes hot, red, swollen and tender, if your baby has a fever, or if they seem unwell rather than simply uncomfortable.

Move a baby with signs of heat exhaustion — unusual tiredness, clamminess, irritability, refusing feeds — somewhere cool immediately, cool their skin, and offer more frequent milk feeds while you seek advice.

What heat rash looks like

Heat rash, also called prickly heat or miliaria, is a rash of tiny spots or bumps that appears where a baby is hottest and least ventilated: the neck folds, the upper back and chest, the shoulders, the armpits, the nappy area, the crook of the elbow and behind the knees, and the forehead under a hat.

The spots may be small and clear like tiny beads of fluid, or small and red. They may look like pinprick bumps in a patch of flushed skin. On brown and black skin the redness is harder to see, so look for the raised texture and check in good light. It can itch or prickle, which is where the name comes from, and babies show that by being restless and rubbing against you.

It appears quickly, often within hours of a baby getting hot, and it fades quickly too. The NHS describes it as not usually serious and says it does not normally need treatment beyond keeping cool.

What causes it

Sweat ducts become blocked, so sweat is trapped under the skin instead of reaching the surface. Babies are prone to it because their sweat ducts are still immature, they have more skin surface for their size, and they cannot take their own clothes off or move away from a heat source.

The common triggers are hot weather, over-dressing, being wrapped in a car seat or sling, a warm bedroom, a fever, and a pram covered with a blanket or muslin. Covering a pram is the one that catches most people out: it stops air circulating and turns the inside into a heat trap.

What actually helps

Cooling is the whole treatment. Take your baby somewhere cooler, remove a layer or two, and let the affected skin have air. Nappy-only time on a towel is the single most effective thing for a neck and chest rash.

A lukewarm bath or a wipe-down with a cool damp cloth helps, then pat dry rather than rubbing, and leave the folds slightly damp to air-dry. Choose loose cotton clothing over synthetics. Dry the neck and skin folds thoroughly after milk, dribble and baths, because moisture sitting in a crease keeps the ducts blocked.

What not to use: thick creams, oils, petroleum jelly and barrier ointments, which block the ducts further, and talcum powder, which is not recommended for babies. Steroid creams are not needed. If skin is very itchy and your baby is scratching, ask a pharmacist rather than reaching for an adult product.

Telling it apart from other rashes

The single most important check is the glass test, and it takes five seconds: press the side of a clear glass firmly against the rash and look through it. Heat rash fades under pressure. A rash that stays visible needs an emergency call, because that is how meningococcal disease presents and the Meningitis Research Foundation asks parents to check every rash this way.

Beyond that, milk spots on a newborn's face are white rather than red and are not related to heat. Newborn acne is red bumps on the cheeks and forehead in the first weeks and comes and goes over months. Eczema is dry, rough and itchy in the creases and persists. Nappy rash is confined to the nappy area and usually spares the deepest creases. Hives are raised weals that move around the body within hours. Chickenpox spots blister and crust and arrive in crops with a fever.

Preventing it

Dress your baby in one more layer than you are comfortable in indoors, and check the chest or back of the neck rather than the hands to judge temperature. Aim for a bedroom between 16 and 20°C, use a sleeping bag with a tog rating suited to the room, and remove hats and outdoor layers as soon as you come inside or get into a warm car.

In hot weather, keep babies under six months out of direct sunlight, use shade and a sunshade that does not block airflow, never cover a pram with a blanket or muslin, and offer more frequent milk feeds — breast milk or formula, not water, for babies under six months. Never leave a baby in a parked car, even briefly.

How long it takes to clear

Heat rash usually improves within a day or two once the cause is removed, and often within hours. Skin that has been scratched can take a little longer. If a rash is still there after several days of genuine cooling, it is probably not heat rash, and that is the point to have it looked at rather than to try another cream.