The clear answer from pediatric and public health organizations is that infants should be placed on their backs for all sleep periods, both naps and at night, until they reach one year of age. This recommendation is the single most effective action parents and caregivers can take to reduce the risk of sudden unexpected infant death (SUID), which includes sudden infant death syndrome (SIDS). The practice of supine, or back, sleeping is based on extensive scientific evidence gathered over decades. This guidance applies to every sleep time, and consistency across all caregivers is important for the baby’s safety.
Understanding the Risks of Prone Sleeping
The primary reason medical professionals advise against prone sleeping is its established link to an increased risk of SIDS, the sudden, unexplained death of a baby under one year old. Studies show that putting a baby to sleep on the stomach can increase the risk of SIDS by a factor of 2 to 13 times compared to back sleeping. This danger is pronounced for babies between one and four months of age, the peak period for SIDS occurrence. The risk is even higher if a baby accustomed to back sleeping is uncharacteristically placed on her stomach for a single sleep.
Several physiological theories explain why the prone position poses a danger. One major concern involves the rebreathing of expired air, especially on a soft surface. When a baby sleeps face-down, she may inhale the carbon dioxide she just exhaled, leading to a buildup of carbon dioxide and a depletion of oxygen in the bloodstream. This effect is magnified if the baby’s face is pressed into a soft mattress or bedding, creating a pocket of stale air.
Prone sleeping is also associated with a diminished ability to regulate body temperature (thermal regulation). Research indicates that babies sleeping on their stomachs are more prone to overheating, which is an independent risk factor for SIDS. Furthermore, the prone position can interfere with the baby’s arousal response, a natural protective mechanism that causes a baby to wake when breathing is compromised. In some SIDS cases, researchers have identified weaknesses in the brainstem responsible for coordinating cardiorespiratory control and arousal. This makes the baby less likely to wake up in response to a breathing challenge.
The widespread adoption of the “Back to Sleep” public health campaign, now known as “Safe to Sleep,” has demonstrated the effectiveness of this intervention. Since the campaign’s launch in the 1990s, the rate of SIDS has declined significantly, in some regions by as much as 50 to 70 percent. This reduction underscores the direct connection between sleep position and infant well-being.
Establishing the Safe Sleep Environment
The chosen sleep position is one element of a comprehensive safe sleep plan; the baby’s environment must also be optimized for safety. The recommended position is flat on the back, on a separate sleep surface, not sharing a bed with parents or other children. Room sharing, where the baby sleeps in the same room as the parents but in a separate, approved space, is recommended for at least the first six months, and ideally for the first year. This practice can reduce SIDS risk by up to 50 percent.
The surface must be firm and flat, such as a mattress in a safety-approved crib or bassinet that does not indent when the baby is lying on it. The mattress should be covered only with a tightly fitted sheet, and no other bedding should be introduced into the sleep space. Soft items like blankets, pillows, bumper pads, stuffed toys, or any other loose objects must be kept out of the crib entirely, as they pose a risk of suffocation or entrapment.
Avoid placing the baby to sleep on soft furniture, such as couches, armchairs, or waterbeds, which increase the risk of sleep-related death. If a parent falls asleep while feeding or comforting the baby in an adult bed, the baby should be moved to her own separate, safe sleep space immediately upon waking. Overheating should also be avoided by keeping the room at a comfortable temperature and dressing the baby in light clothing. A wearable blanket or sleep sack is a safer alternative to loose blankets for keeping the baby warm.
Addressing Developmental Milestones and Position Changes
A common concern arises when a baby begins to achieve the developmental milestone of rolling over, typically between four and six months of age. It is important to always place the baby to sleep on her back, even as she approaches this stage.
Once a baby can reliably roll from the back to the stomach and back again, parents do not need to repeatedly reposition the baby during sleep. If the baby rolls onto her stomach after being placed on her back, she has demonstrated the strength and motor control necessary to move her head and adjust her position to breathe. However, the crib environment must remain free of all soft bedding and loose objects so that the baby’s face does not become obstructed.
This transition period is also when parents must stop swaddling the baby, as soon as the baby shows the first signs of attempting to roll. Swaddling a baby who can roll is unsafe because it restricts the use of her arms, which are needed to push up and reposition her head if she rolls onto her stomach.
During the day, supervised “Tummy Time” remains an important, separate activity that helps the baby develop the neck, shoulder, and back muscles needed for rolling and crawling. Tummy Time should occur when the baby is awake and alert, starting with short, frequent sessions from birth and gradually increasing to 15 to 30 minutes daily by about two months of age.