Can my baby sleep in just a vest?

The verdict

Yes. In a room above 20°C, a short sleeve bodysuit is what the Lullaby Trust actually recommends, and in genuinely hot weather it says it is fine to have your baby in a short sleeve vest or even just a nappy.

The instinct to add layers is the one to resist. The Lullaby Trust states the direction of error plainly: research shows that babies are safer being cooler than being too hot. Overheating is an established SIDS risk factor. Being slightly cool is not.

What to put them in, by room temperature

The Lullaby Trust ties clothing to the room rather than to a chart on a packet, and its four bands are the clearest published version of this advice anywhere.

Cooler than 16°C. Add a clothing layer, or use a higher tog sleeping bag. Do not add blankets on top of a sleeping bag – air trapped between layers increases the warmth unpredictably.

16 to 20°C, the recommended range. A baby grow with a well-fitting sleep bag, or a baby grow with a firmly tucked in lightweight blanket. Either is fine.

Warmer than 20°C. A lightweight layer such as a short sleeve bodysuit.

Really hot weather. A short sleeve vest, or just a nappy.

Red Nose Australia gets to the same place from the other direction. It declines to publish a room temperature at all, on the basis that there is no evidence a specific room temperature prevents sudden infant death, and asks you to dress baby as you would dress yourself: if you are comfortable, neither too hot nor too cold, dress baby the same way.

The check that actually tells you

Not the thermostat, and not their hands. Feel the chest, the tummy or the back of the neck. The Lullaby Trust notes that a baby's hands and feet will usually be cooler, and that this is normal. Red Nose says the same about hands, ears, cheeks and noses – the core is what you are reading. If the skin is hot or sweaty, take a layer off. If the tummy feels cool, add one.

Hoods, hats and the thing most people get wrong

This is where the garment question stops being about warmth and becomes a safety question, and it is where sleepwear is most often chosen badly.

Babies mainly control their temperature by releasing heat through the head and face. Cover the head and you remove their main route for shedding heat, at the same time as adding a risk of the covering slipping over the face.

The Lullaby Trust is direct: babies do not need hats indoors as they can overheat. Red Nose is more emphatic still – always remove head coverings for sleep, and remove hats, bonnets, beanies and hooded clothing from baby's head as soon as baby is indoors. Its guidance on covered heads states that covering a baby's face or head during sleep significantly increases the risk of SUDI, because it can block or restrict the airway, cause rebreathing of the same air, lead to overheating, and create hazards such as strangulation or entrapment where items like headbands, ribbons or loose fabrics are present.

Practically, that rules out three things people buy without thinking: hooded sleepsuits, sleeping bags with hoods, and pram suits or snowsuits left on for a nap indoors or in a car seat.

What to look for in a sleepsuit

No hood. No loose ribbons, ties or drawstrings anywhere near the neck. Nothing that can be pulled up over the face. A fit that is snug rather than baggy at the neck. Integrated feet are fine and useful; what matters is that they are not tight enough to cramp the toes, because the bones in a baby's toes are soft and can be prevented from growing straight by cramped socks or sleepsuits.

If you use a sleeping bag rather than blankets, the Lullaby Trust asks for one that is well fitted at the neck and shoulders so a baby cannot wriggle down inside it, and Red Nose asks for a fitted neck, arm holes with arms free, and no hood. Sleeping bags are sized by weight rather than age for exactly this reason.

Hot nights, and what to do when the room will not cool

The Lullaby Trust's hot-weather advice assumes you will sometimes fail to hit 16 to 20°C, and tells you what to do anyway: lighter bedding and clothing with fewer layers, open the bedroom door and a window if it is safe, keep curtains closed during the day so the room heats less, and use a fan to cool the room without aiming it directly at the baby. Keep the cot away from radiators, direct sunlight and heaters.

And then the sentence that gives most parents permission: in really hot weather, it is fine to have your baby in a short sleeve vest or even just a nappy. You are not doing anything wrong by undressing them.

When your baby is unwell

The temptation is to wrap a poorly baby up. The Lullaby Trust says the opposite: dress your baby for their environment, and resist the temptation to wrap an unwell baby up more than usual. A baby with a fever is already running warm, and adding layers on top of that compounds the risk rather than helping.

Where guidance differs

The UK names temperatures; Australia refuses to. The Lullaby Trust recommends 16 to 20°C and a room thermometer. Red Nose says there is no evidence that a specific room temperature prevents sudden infant death, and that it does not believe a room temperature monitor is necessary. Both then give the same body-check instruction, which is the part that actually generalises.

The American position makes clothing carry more weight. Because the AAP excludes blankets from the sleep space under twelve months, the clothing layer and a wearable blanket do the whole job in the United States. In the UK and Australia a tucked-in blanket can take up the slack, so the clothing choice is less critical.

On heads, everyone agrees completely. No hats indoors, no hoods for sleep, nothing over the face. If you take one thing from this page rather than a temperature band, take that.