Sudden Infant Death Syndrome: What is it, what causes it, and how to prevent it

SIDS, also known as cot death, affects mainly babies in their first six months of life...

Image of baby legs seen through cot bars

Sudden Infant Death Syndrome is widely recognised as ‘cot death’ and is the main reason all new parents obsess over checking that their baby is still breathing.

Trigger warning: Sudden Infant Death Syndrome is a hard subject to read about, but here at we are dedicated to arming you with the factually correct information, for you to make informed decisions that are right for you and your family. 

Statistically Sudden Infant Death Syndrome affects babies in the first six months of their lives, causing the death of nearly 200 babies in the UK each year. It's characterised by the sudden, unexpected and unexplained death of an apparently healthy baby, usually while they’re sleeping.

It’s the not knowing that makes it terrifying for parents and carers. Dr Nauf AlBendar (opens in new tab), Medical Scientist & founder of The Womb Effect says, "Although the cause is still unknown, evidence suggests that a combination of physical and environmental factors can make an infant more vulnerable to SIDS."

And, while there are no symptoms as such that parents can look out for, there are guidelines to be aware of which highlight what you can do to avoid SIDS and lower the risk.

Sudden Infant Death Syndrome - what is it and what causes it?

Sudden Infant Death Syndrome is sometimes referred to and recognised as ‘cot death’. It’s the sudden, unexpected and unexplained death, usually during sleep according to research, of an otherwise outwardly healthy baby. This tends to happen to infants under the age of 12 months. The exact cause of SIDS is unknown.

Incidences of SIDS has dropped tremendously since the launch of the Safe to Sleep (formerly known as 'Back to Sleep') campaign in 1994. Yet the NHS reports about 200 sudden and unexpected infant deaths each year.

Though, 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 out at risk in certain conditions, such as a smoke filled room. In addition, bedding and choice of bed can be a huge factor.

A study from 2018 mentions that one theory for SIDS is nervous system “abnormalities.” Meaning changes in the infant’s nervous system occur at around 2–4 months, a period when SIDS is most likely to occur.

However, this is currently only a theory, and there is little evidence to confirm it as a cause for SIDS. Other factors to add to contribute to a higher risk of SIDS includes tobacco smoke, baby getting tangled in bedding, a minor illness or a breathing obstruction. 

There has also been a long-standing association between co-sleeping (sleeping with your baby on a bed, sofa or chair) and SIDS. Babies who die of SIDS are thought to have problems in the way they respond to these external factors. Along with how they regulate their heart rate, breathing and temperature - internal factors.

Although the cause of SIDS is not fully understood, there are a number of things carers can do to reduce the risk.

Dr Nauf AlBendar (opens in new tab), Medical Scientist & founder of The Womb Effect says, "Although the cause is still unknown, evidence suggests that a combination of physical and environmental factors can make an infant more vulnerable to SIDS.

"Researchers refer to the Triple-Risk Model to explain this concept. In this model, all three factors have to occur for an infant to die from SIDS. These are:

  • Being at risk: When the baby has an unknown problem such as having a defect in the portion of their brain that controls breathing, heart rate, blood pressure, temperature, and waking from sleep.
  • Being in a sensitive time of development: During the first 6 months after birth, infants go through many quick phases of growth that can change how well the body controls or regulates itself, as they learn how to respond to their environment.
  • Stressors in the environment: These can include sleeping on the stomach, overheating during sleep, having things in the cot that could interfere with breathing and exposure to secondhand smoke."

So while the exact causes of SIDS have yet to be discovered, there are some things you can do to reduce the risk. This could include having a suitable and safe cot for your baby to sleep in the same room as you (you could also have them sleep in a good quality moses basket), and remove any extra items from their cot which could create a hazard.

Are there any warning signs of Sudden Infant Death Syndrome?

No, there are no obvious warning signs of SIDS. Research suggests that the condition is slightly more common in baby boys and premature babies, putting both in these categories at a higher risk, respiratory infections is another which could contribute to breathing problems. And factors such as race and gender should be taken into account.

According to research by The Lullaby Trust just over half (55.3%) of all unexplained infant deaths were boys in 2019 (0.29 deaths per 1,000 live births). This is a decrease from 57.6% in 2018. And, Dr AlBendar tells us, "There are some factors to consider such as the baby being low birth weight or preterm. This could increase the likelihood of baby’s brain not having matured completely, thus having less control over automatic processes such as breathing and heart rate.

 "Respiratory infections is another which could contribute to breathing problems. And factors such as race and gender should be taken into account."

 The best way to help your baby to sleep more safely is by following the safety regulations mentioned above for SIDS prevention, such as "placing the baby to sleep on his or her back and in the same room, keeping the cot as bare as possible and avoiding overheating the baby."

 If you’re worried about your baby, visit your GP or health practitioner who will be able to give more insight into the condition and offer solutions to other baby sleep problems.

How can SIDS be prevented?

While there’s no clear cut way to prevent SIDS, it’s suggested that your baby's sleep area (for example, a cot or Moses basket) is in the same room where you sleep until your baby is at least 6 months old, or ideally, until your baby is one year old. 

Keep soft bedding such as blankets, pillows, bumper pads, and soft toys out of your baby's sleep area.

Until baby is at least 6 months old, they should be put down to sleep on their back, according to research by BMC Pediatrics

The Lullaby Trust, specialises in safer baby sleep and raises awareness on sudden infant death, they have a helpful video to outline how to keep your baby bed safe.

Enough is now known about Sudden Infant Death Syndrome for parents to dramatically reduce the risk. The following tips will help to reduce the risk of 'cot death' and put your mind at rest.

  1. Lie your baby down on their back to sleep.
  2. Place them 'feet to foot'. Their feet should reach the end of the cot, with blankets to their chest and firmly tucked in bedding, nothing loose.
  3. Don't let your baby overheat: never place a cot next to a radiator; don't use a duvet or any headwear and keep your baby's room between 16-20 degrees.
  4. Don't smoke in pregnancy or around a young baby.
  5. Keep the baby's cot in your room for the first six months and ensure that it meets the UK's cot safety guidelines.
  6. Use a firm, flat mattress for your baby. No pillows, bean bags or water beds.
  7. Don't fall asleep on an armchair or sofa with your baby - you might smother them.
  8. If your baby is unwell, contact your doctor promptly.
  9. Keep your baby's head uncovered, don't tuck their blanket too high and make sure it's never above their shoulders.
  10. Breastfeed if possible.
  11. Don’t co-sleep if you have been smoking or drinking beforehand.

At what age does cot death stop being an issue?

The risk of SIDS drops after the age of 1. While having a young baby that could be vulnerable to SIDS is a worrying thing for parents, our expert Dr AlBendar says that infants are most vulnerable between the second and fourth months of life.

She says, "It tends to decrease after 6 months, and it's extremely rare after the age of one."

Is it okay to swaddle my baby?

Yes, but swaddling can be a contributing factor to SIDS. And if you wish to swaddle here’s how to do it correctly; such as never put a swaddled baby to sleep on their front or side, don’t swaddle if bed-sharing, stop swaddling (with arms wrapped inside the material) when a baby shows signs of rolling as they could roll onto their front and get stuck. 

Swaddling is a traditional practice of wrapping a baby in a blanket tightly, to keep them from moving too much during the night. Recent research has found that this could potentially be harmful, and a possible contributing factor to SIDs.

Dr Anna Pease, lead author of a study at University of Bristol that looked into the causes of SIDs, said, "We tried to gather evidence of whether there was an association between swaddling for sleep and SIDS.

"The risk of SIDS when placing infants on the side or front for sleep increased when infants were swaddled." The current recommendation advises not placing your child on its side or front for sleep, and this would appear especially important if you have swaddled your baby.Anna advises parents that, "most babies start being able to roll over at about four to six months.

"On a practical level what parents should take away from this is that if they choose to swaddle their babies for sleep, always place them on their back, and think about when to stop swaddling for sleep as their babies get older and more able to move."

Do sleeping bags increase risk of SIDS?

No, baby sleeping bags (opens in new tab) are very safe, according to research (opens in new tab). As they help a baby maintain a constant temperature, therefore helping prevent Sudden Infant Death Syndrome. A sleeping bag should comply to British Safety Standards (BS 8510:2009) and you should always check it the first time you use it and periodically thereafter.

Make sure that the seams don’t have any sharp edges, that the zips are secure and there are no attachments such as buttons that could fall off and they could choke on. ‘It is recommended that you avoid buying a sleeping bag with arms or a hood as there is a serious risk of your baby overheating,’ Vickie Bowles (opens in new tab) of The Baby Academy tells us.

Can co-sleeping with my baby increase the risk of SIDS?

Bed sharing with your baby, otherwise known as co-sleeping, increases the risk of SIDS and the risk is particularly increased when:

  • Either parent smokes even if they don&'t smoke in the bedroom or anywhere in the house
  • Either parent has consumed alcohol or taken drugs (including medication that may make you drowsy)
  • The baby is premature
  • The baby was a low birth weight

The safest place for a baby to sleep for the first six months is a separate cot or Moses basket in the same room as the parents.

Will giving my baby a dummy reduce the risks of SIDS?

There is no definitive research to say whether dummies reduce the risks of SIDS, according to a 2019 study. Dummies aren't a means of prevention as such, but they are associated with a reduced risk of 'cot death'. Experts don't yet know why dummies help in babies who are used to them, but the statistics prove they do. And dummy-users who suddenly stop are at increased risk of SIDS.

These findings, while slightly confusing for parents, basically mean that if your baby uses a dummy, they should carry on doing so.

So if your baby has a dummy, be sure to use it every night. It's thought that it may help by creating more air space if a baby's face gets under a blanket. But this doesn't wholly explain the difference between users and non-users, so there's no reason for you to introduce a dummy as a means of prevention.

On the whole, even the best quality sleep aids won't prevent SIDS but ones such as black-out blinds and night lights could help your baby get a better night's sleep without interfering with their sleeping space.

Does formula increase the risk of SIDS?

No. Dr AlBendar says, "if you follow the safety regulations for SIDS prevention, then chances are extremely low."

Although research has demonstrated that exclusively breastfeeding and even combination feeding (breast milk and formula) for up to four months can reduce SIDS risk by 40 per cent, it won’t exclusively reduce SIDS. 

In addition, The Lullaby Trust states It has been shown that partial or combination feeding (breast milk and formula) and exclusive breastfeeding have been associated with lower SIDS rates. Thankfully SIDS is now very rare. If you bottle feed your baby and follow all the other pieces of safer sleep advice then the chance of SIDS is extremely low.

Seeking medical advice if your baby is unwell

There are lots of minor illnesses that babies can suffer from that are absolutely nothing to be seriously worried about. But if your little one is showing some of the following symptoms you should dial 999 for an ambulance:

  • Stops breathing or turns blue
  • Struggling for breath
  • Unconscious and seems dazed
  • Won't wake up
  • Has a fit

The Lullaby Trust also has a helpful guide called the Baby Check booklet which includes a checklist of symptoms to help you understand if your baby is ill.

If you are in any doubt about your child's health, be sure to book an appointment ASAP with your GP or local health practitioner.

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