The sudden and unexpected death of a baby is usually referred to as ‘sudden unexpected death in infancy’ (SUDI) or ‘sudden unexpected death in childhood’ (SUDC), if the baby was over 12 months old. 

Some sudden and unexpected deaths can be explained by the post-mortem examination, revealing, for example, an unforeseen infection or metabolic disorder. Deaths that remain unexplained after the post-mortem are usually registered as ‘sudden infant death syndrome’ (SIDS) or SUDC in a child over 12 months.

What causes SIDS?

We do not know what causes SIDS. For many babies it is likely that a combination of factors affect them at a vulnerable stage of their development, which leads them to die suddenly and unexpectedly.

However, we do know you can significantly reduce the chance of SIDS occurring by following safer sleep advice.

Around 89% of SIDS deaths happen when a baby is six months old or less.

To reduce the risk of SIDS for your baby, follow the Lullaby Trust's evidence-based safer sleep advice –such as sleeping your baby on their back in a clear cot or Moses basket – for the first six months.

After this time, the risk is reduced, however SIDS can still happen so it is best to continue the safer sleep routines you have built up over time.

Why don’t we use the term ‘cot death’?

‘Cot death’ was a term commonly used in the past to describe the sudden and unexpected death of an infant. It has largely been abandoned, due to its misleading suggestions that sudden infant death can only occur when a baby is asleep in their own cot, which we know to be untrue.

Is SIDS common?

While SIDS is comparatively rare – 216 babies died of SIDS in the UK in 2015 – it can still happen and there are steps you can take to help reduce the chance of it occurring.

Can SIDS be prevented? What are the biggest risk factors?

While SIDS cannot be completely prevented, you can reduce the risks of it occurring considerably by following The Lullaby Trust's safer sleep advice. For example:

  • Sleep your baby on their back for all sleeps – day and night – as this can reduce the risk of SIDS by six times compared to sleeping them on their front.
  • Share a room with your baby for the first six months – this can halve the risk of SIDS.
  • Keep your baby smoke-free during pregnancy and after birth – this is one of the most protective things you can do for your baby. Around 60% of sudden infant deaths could be avoided if no baby was exposed to smoke during pregnancy or around the home.
  • Never sleep on a sofa or armchair with your baby as this can increase the risk of SIDS by 50 times.
  • Do not co-sleep with your baby if you or your partner has been drinking, is a smoker, has been taking drugs or is extremely tired; these factors can put babies at an extremely high risk of SIDS when co-sleeping. One study found that the risk of SIDS when co-sleeping is six times higher in smokers than in non-smokers.

The above is especially important for babies who were born premature or of low birth weight, as these babies are at a higher risk of SIDS.