Safe sleep environment

Sleep-related infant deaths are rare in Sweden, but research has shown that the sleep environment plays a significant role in further reducing risk. In Sweden, cases have decreased from about 120 per year in the 1990s to around 15, largely thanks to changed sleeping habits and targeted guidance.¹

The term SIDS (sudden infant death syndrome) refers to deaths that remain unexplained after a complete investigation. The guidelines below apply to a broader spectrum of sleep-related risks, which also includes suffocation and other accidents in the sleep environment.² ³

Back sleeping

Back sleeping is the single most important protective factor. Both the Swedish National Board of Health and Welfare and 1177 Vårdguiden recommend that infants should always sleep on their back.¹ ⁴ Sweden was one of the first countries to recommend back sleeping, as early as the late 1980s, and mortality has since decreased by over 80 %. Internationally, similar campaigns (such as the US "Back to Sleep" in 1994) led to reductions of over 50 % in most countries. The recommendation applies to all sleep occasions, including naps.⁵

Is side sleeping safe?

Side sleeping is discouraged by both Swedish and international child health organisations.³ ⁴ A systematic review by Gilbert et al. (2005) found that stomach sleeping increased the risk roughly four- to fivefold compared with back sleeping, while side sleeping roughly doubled it.⁶ The main reason side sleeping is discouraged is that it is an unstable position: a child who cannot yet roll back risks ending up on the stomach. But side sleeping is also considered a risk factor in itself. The exact mechanisms are not fully understood, but suggested explanations include altered airway geometry and reduced arousal reflexes compared with back sleeping.³

It is common for babies to prefer sleeping on their side, or to fall asleep in a side position during breastfeeding. Ending up on the side after being placed on the back is not uncommon, especially from 3 to 4 months of age as motor development accelerates.

The recommendation is clear: always place the child on their back for sleep. According to the AAP (2016), the parent does not need to reposition the child if they can roll in both directions on their own.⁵ The NHS and Red Nose give similar advice.⁷ ⁸ In the AAP's 2022 update the recommendation that back sleeping should be used for every sleep onset is repeated, but the wording about rolling is less specific.³

In practice this means the most important thing is to always place the child on their back, and that a child with good head control who actively chooses position is at lower risk. The phase when a child can roll one way but not back is usually short.

If the child repeatedly ends up on its side, for example during nighttime breastfeeding, it is important that the rest of the sleep environment is as safe as possible: firm mattress, no loose pillows or blankets near the child's face.

Side sleeping can also increase the risk of positional plagiocephaly (flat head) on the side the child prefers. Varied head position during waking hours and regular tummy time can prevent this.⁹

Smoking and alcohol

Smoking during pregnancy and passive smoking after birth are strong risk factors for sleep-related infant death. Nicotine and other substances in tobacco smoke affect brain development in the foetus, including the areas that control breathing and arousal reflexes. This means the child may have more difficulty responding to oxygen deprivation or other disturbances during sleep. Passive smoking after birth also increases the risk, partly through effects on the airways. The risk increases with the number of cigarettes and applies to both parents' smoking. The Swedish National Board of Health lists smoke-free environments as one of the most important preventive measures.⁵ ¹

Alcohol and drug use by parents also increases the risk, particularly in combination with bed-sharing. Alcohol impairs the parent's ability to respond to the child during sleep and increases the risk of the parent rolling onto the child. All major organisations (AAP, UNICEF, Lullaby Trust and Red Nose) advise against bed-sharing if either parent has consumed alcohol.³ ¹⁰ ¹¹ ⁸

Sleep space

The child should sleep on a firm, flat mattress without pillows, blankets or loose objects. Cot bumpers are common in Sweden and not subject to the same strong discouragement as in the US (where the AAP advises against them entirely). If cot bumpers are used they should be thin, firm and securely fastened so the child cannot press their face against them or become trapped.¹²

A sleep sack is an alternative to loose blankets and is becoming increasingly common in Sweden, although it is not included in Swedish guidelines. In the US, the AAP recommends sleep sacks as a replacement for loose blankets³, and in the UK the Lullaby Trust gives the same advice.¹¹ The advantage is that the child's face is not at risk of being covered during sleep. If a sleep sack is used it should be the right size so the child cannot slide down inside it.

Research on sleep sacks and the risk of sleep-related infant death is limited but promising. A Dutch case-control study found that sleep sacks were associated with approximately 65 % lower risk, partly because the children less often ended up in the prone position.¹³ An English study showed a similar trend, but after adjustment for other factors the association could not be confirmed as statistically significant.¹⁴ Overall, there is not yet sufficient evidence to conclude that sleep sacks in themselves protect, but they reduce exposure to loose blankets, which is an established risk factor.

Swaddling

Swaddling – wrapping the baby in a blanket or special swaddle – is a widespread tradition in many cultures that can soothe newborns and reduce crying, including for colic. Research shows that swaddling can extend sleep slightly and reduce spontaneous awakenings.¹⁵

The main risk with swaddling is related to sleep position and age. A meta-analysis by Pease et al. (2016) showed that swaddled babies who ended up in the prone position had a substantially increased risk of sleep-related infant death, and side sleeping also carried a clear risk increase. In the supine position the risk was only marginally increased, and the result should be interpreted with caution as the studies were small and observational. The risk also appeared to increase with the child's age, probably because older infants can more easily roll out of the supine position.¹⁶

There is also some research suggesting that swaddling may reduce arousal sensitivity, which is theoretically a risk factor, but the effect was small and inconsistent across studies.¹⁷

In practice this means swaddling can be used during the first months, as long as the child is always placed on their back and swaddling is discontinued as soon as the child shows signs of being able to roll (usually around 2 to 4 months of age). Internationally, guidelines are consistent: the AAP (US) does not take a position for or against swaddling but gives safety advice³, the Lullaby Trust (UK) accepts swaddling with clear guidelines¹⁸, and Red Nose (Australia) describes it as a useful strategy for helping babies fall asleep on their backs during the early months.¹⁹ All emphasise that swaddling should not be too tight around the hips (risk of hip dysplasia) or too loose (the fabric may cover the face), and that swaddling should be avoided during bed-sharing or fever. Overheating should also be considered, especially in warm rooms. Use thin material and do not dress the child too warmly under the swaddle.¹¹ In Sweden, neither the National Board of Health nor 1177 Vårdguiden mention swaddling in their safe sleep guidelines, meaning it is neither recommended nor advised against.

Temperature

Overheating is a known risk factor for sleep-related infant death and should be avoided. Many guidelines mention 18 to 20 °C as a guide, but there is no exact threshold. In warmer climates or homes with higher indoor temperatures, the child's clothing is instead adjusted so that the child does not have more layers than necessary to feel comfortably warm. Signs of overheating may include sweaty hair, a damp chest or a warm neck. Avoid hats and excessive blankets indoors.¹²

Room-sharing

Room-sharing (the child sleeping in their own bed in the parents' room) is recommended for at least the first 6 months. Being close to the parent makes it easier to notice and respond to changes in the child's breathing, movements or sounds. There is also a theory that the parent's presence (sounds, movements and scent) stimulates the child's arousal reflexes and contributes to more regular breathing. Studies show that the risk of sleep-related infant death is lower with room-sharing compared with the child sleeping in a separate room.²⁰

Pacifier

Pacifier use at sleep onset has been associated with a reduced risk of sleep-related infant death in several studies, although the mechanism is not fully understood. It is recommended not to force the pacifier if the child does not want it, and not to replace it if it falls out during sleep.²¹

White noise

White noise (or pink noise, brown noise and similar) is primarily used to mask sudden sounds that might wake the baby. A study (2014) tested 14 white noise machines and found that all could exceed recommended sound levels at close range. The study authors recommend a maximum sound level of 50 dB (roughly equivalent to a quiet conversation) and that the sound source is placed at least one metre from the baby.²²

About the sources

The information on this page is based primarily on published research. Guidelines from various organisations, such as the Swedish National Board of Health and 1177 Vårdguiden (Sweden)¹ ⁴, the AAP (US)³, NICE and UNICEF Baby Friendly Initiative (UK)⁷ ¹⁰, and Red Nose (Australia)⁸, are used as supplements. US guidelines tend to be more restrictive than European ones; for example, the AAP advises entirely against bed-sharing, while British and Swedish guidelines give more nuanced advice based on individual risk assessment.