Sudden infant death syndrome (SIDS), also known as cot death, is the sudden, unexpected and unexplained death of an apparently well baby.
Most deaths happen during the first three months of a baby’s life. Infants born prematurely or with a low birth weight are at greater risk, and SIDS is also more common in baby boys.
Most unexpected deaths occur while the child is asleep in their cot at night. However, SIDS can also occur when a baby is asleep during the day or, occasionally, while they are awake.
Mothers 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).
No one knows exactly what causes SIDS, but it is thought to be the result of 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 due to being born prematurely or to low birth weight, or other reasons not yet identified.
Environmental stresses could include tobacco smoke, getting tangled in bedding, minor illness or having 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 is not fully understood, you can reduce the risk (see below).
Follow the advice below to help prevent SIDS.
Exposure to cigarette smoke can significantly increase your baby's risk of dying suddenly and unexpectedly. This applies to mothers who smoke during pregnancy and after the birth and also to those smoking around the baby.
If you smoke during pregnancy, your baby is four times more likely to die from SIDS than if you don't.
If your baby is exposed to a smoky environment after they are born, they are eight times more likely to die from SIDS compared to an infant living in a smoke-free environment.
If you smoke, your doctor can recommend appropriate treatment and local support services to help you quit.
Read more information and advice about giving up smoking.
It is important that you seek help and support if your baby has died suddenly and unexpectedly.
There will need to be an investigation into how and why your baby died, conducted by a coroner (a judicial officer) and a post-mortem examination will usually be required. This can be very distressing for the family.
The police and healthcare professionals work closely to investigate unexpected infant deaths and ensure 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 cope with their bereavement.
The Lullaby Trust provides advice and support for bereaved families. You can also visit their website for further bereavement information and advice.
The babyloss and Sands websites are also useful resources for those affected by the death of a baby during pregnancy, at birth or shortly afterwards.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.