Sudden infant death syndrome (SIDS)

Sudden infant death syndrome (SIDS) – sometimes known as "cot death" – is the sudden, unexpected and unexplained death of an apparently healthy baby.

About SIDS

SIDS is rare and the risk of your baby dying from it is low.

Most deaths happen during the first six months of a baby’s life. Infants born prematurely or with a low birthweight are at greater risk. SIDS also tends to be slightly more common in baby boys.

SIDS usually occurs when a baby is asleep, although it can occasionally happen while they're awake.

Parents can reduce the risk of SIDS by not smoking while pregnant or after the baby is born, and always placing the baby on their back when they sleep (see below).

Causes of SIDS

The exact cause of SIDS is unknown. It's thought to be down to a combination of factors.

Experts believe SIDS occurs at a particular stage in a baby’s development, and that it affects babies who are vulnerable to certain environmental stresses.

This vulnerability may be caused by being born prematurely or having a low birthweight, or because of other reasons not yet identified. 

Environmental stresses could include tobacco smoke, getting tangled in bedding, a minor illness or a breathing obstruction. 

Babies who die of SIDS are thought to have problems in the way they respond to these stresses and how they regulate their heart rate, breathing and temperature.

Although the cause of SIDS isn't fully understood, there are a number of things you can do to reduce the risk, see the sections below.

The risks of co-sleeping

The safest place for your baby to sleep for the first 6 months is in a cot in your room.  Sharing a bed with your baby is associated with a higher risk of SIDS. If you bring your baby into bed to breastfeed, put them back to sleep in their cot after feeding.

Speak to your midwife, health visitor, family nurse or GP for advice if you feel strongly that you wish your baby to sleep with you instead of in a cot or Moses basket. They can help you understand the increased risks.

If you decide to take a baby into your bed, make sure you or your partner have not taken any medicine, drugs or alcohol that may make you sleep more heavily than usual.

You should never sleep with your baby on an armchair or sofa. If you are feeling tired or sleepy put the baby back in their cot in case you fall asleep.

How to help reduce the risk of SIDS

Below is a list of things you can do to help prevent SIDS.


  • always place your baby on their back to sleep
  • place your baby in the "feet to foot" position (with their feet touching the end of the cot, Moses basket, or pram)
  • keep your baby’s head uncovered - use a light blanket firmly tucked no higher than the baby’s shoulders
  • let your baby sleep in a cot or Moses basket in the same room as you for the first six months
  • if using a baby sleeping bag, make sure it is fitted with neck and armholes, and no hood
  • use a mattress that's firm, flat, waterproof and in good condition
  • breastfeed your baby (if you can) and put your baby back to sleep in their cot after feeding

Do not:

  • smoke during pregnancy or let anyone smoke in the same room as your baby (both before and after birth)
  • sleep on a sofa, or armchair with your baby
  • allow your baby to sleep alone in an adult bed
  • allow your baby to share a bed with anyone who has been smoking, drinking alcohol, taking drugs or is feeling overly tired
  • let your baby get too hot or too cold- a room temperature of 16C to 20C, with light bedding or a lightweight baby sleeping bag, will provide a comfortable sleeping environment for your baby
  • leave your baby sleeping in a car seat for long periods or when not travelling in the car
  • put pillows, loose blankets, cot bumpers or sleep positioners in your baby’s cot


Seeking medical advice if your baby is unwell

Babies often have minor illnesses that you don't need to worry about. Give your baby plenty of fluids to drink and don't let them get too hot.

If you're worried about your baby at any point, see your GP or contact GP out of hours service for advice.

Dial 999 for an ambulance if your baby:

  • stops breathing or turns blue
  • is struggling for breath
  • is unconscious or seems unaware of what's going on
  • won't wake up
  • has a fit for the first time, even if they seem to recover

Support services

If a baby dies suddenly and unexpectedly, there will need to be an investigation into how and why they died. A post-mortem examination will usually be necessary, which can be very distressing for the family.

The police and healthcare professionals work closely to investigate unexpected infant deaths and make sure the family is supported. They should be able to put you in touch with local sources of help and support.

Many people find talking to others who have had similar experiences helps them to cope with their bereavement.

The Lullaby Trust provides advice and support for bereaved families.

The information on this page has been adapted from original content from the NHS website.

For further information see terms and conditions.

This page was published August 2018

This page is due for review November 2021

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