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It's not known why some babies die suddenly and for no apparent reason from sudden infant death syndrome (SIDS), or cot death.

Experts do know placing a baby to sleep on their back reduces the risk, and exposing a baby to cigarette smoke or allowing them to overheat increases the risk. 

It's also known there's an association between sleeping with your baby on a sofa or chair and SIDS.

Follow the advice on this page to reduce the risks as much as possible.

To reduce the risk of SIDS:

• place your baby on their back to sleep, in the same room as you, for the first 6 months
• keep your baby's head uncovered – their blanket should be tucked in no higher than their shoulders
• if wearing your baby in a sling or carrier, do not cover their head with the sling material or with a muslin
• place your baby in the "feet to foot" position, with their feet at the end of the cot or Moses basket
• do not let your baby get too hot or cold
• never sleep with your baby on a sofa or armchair
• do not smoke when you're pregnant or around your baby after they're born, and do not let anyone smoke in the same room as your baby

Place your baby on their back to sleep from the very beginning for both day and night sleeps. This will reduce the risk of cot death.

Do not put your baby to sleep on their side or tummy.

Once your baby is old enough to roll over, there's no need to worry if they turn onto their tummy or side while sleeping.

Babies whose heads are covered with bedding are at an increased risk of SIDS.

To prevent your baby wriggling down under the covers, place them in the "feet to foot" position. This means their feet are at the end of the crib, cot or Moses basket.

To put your baby in the feet to foot position:

• tuck the covers in securely under your baby's arms so they cannot slip over their head – use 1 or more layers of lightweight blankets
• use a baby mattress that's firm, flat, well-fitting, clean and waterproof on the outside – cover the mattress with a single sheet
• do not use duvets, quilts, baby nests, wedges, bedding rolls or pillows

If you use a sling or carrier, make sure you use it safely.

The Lullaby Trust has more information and advice about swaddling your baby and using slings

Overheating can increase the risk of SIDS. Babies can overheat because of too much bedding or clothing, or because the room is too hot.

• When you check your baby, make sure they're not too hot. If your baby is sweating or their tummy feels hot to the touch, take off some of the bedding. Do not worry if their hands or feet feel cool – this is normal.
• It's easier to adjust for the temperature by using layers of lightweight blankets. Remember, a folded blanket counts as 2 blankets. Lightweight, well-fitting baby sleeping bags are a good choice, too.
• Babies do not need hot rooms. All-night heating is rarely necessary. Keep the room at a temperature that's comfortable – about 16 to 20C is ideal.
• If it's very warm, your baby may not need any bedclothes other than a sheet.
• Even in winter, most babies who are unwell or feverish do not need extra clothes.
• Babies should never sleep with a hot water bottle or electric blanket, next to a radiator, heater or fire, or in direct sunshine.
• Babies lose excess heat through their heads, so make sure their heads cannot be covered by bedclothes, slings or carriers while they're asleep.
• Remove hats and extra clothing as soon as you come indoors or enter a warm car, bus or train, even if it means waking your baby.

If you share a bed with your baby (co-sleeping), you should:

• make sure they sleep on a firm, flat mattress lying on their back
• not have any pillows or duvets near them
• not have other children or pets in the bed at the same time

It's important not to share a bed with your baby if they had a low birthweight (less than 2.5kg or 5.5lb) or if you or your partner:

• smoke (no matter where or when you smoke and even if you never smoke in bed)
• have had 2 or more units of alcohol
• have taken recreational drugs
• have taken medicine that causes drowsiness

It's lovely to have your baby with you for a cuddle or a feed, but sleeping with your baby on a sofa or armchair is linked to a higher risk of SIDS. 

It's safest to put your baby back in their cot before you go to sleep.

Babies exposed to cigarette smoke before and after birth are at an increased risk of SIDS. Do not let anyone smoke in the house, including visitors.

Ask anyone who needs to smoke to go outside. Do not take your baby into smoky places.

If you smoke, sharing a bed with your baby increases the risk of cot death.

Get help and support if you want to quit smoking

Breastfeeding your baby reduces the risk of SIDS.

It's possible using a dummy at the start of a sleep also reduces the risk of SIDS. But the evidence is not strong and not all experts agree that dummies should be promoted.

If you do use a dummy, do not start until breastfeeding is well established. This is usually when your baby is around 1 month old.

Stop giving them the dummy when they're between 6 and 12 months old.

Babies often have minor illnesses that you do not need to worry about.

Give your baby plenty of fluids to drink and do not let them get too hot. If your baby sleeps a lot, wake them up regularly for a drink.

It can be difficult to judge whether an illness is more serious and needs urgent medical attention.

See spotting the signs of serious illness for guidance on when to get help.