A baby should always be placed flat on their back, on a firm mattress, in a crib with nothing else in it. This single practice, consistently followed for every sleep, reduced SIDS deaths by over 50% in the decade after it became the standard recommendation in the United States. The back position is safest for all babies until their first birthday, including preterm infants and those with reflux.
Why Back Sleeping Is Safest
When a baby sleeps on their stomach, the risk of overheating increases, and they’re more likely to rebreathe air they’ve already exhaled. That trapped carbon dioxide and reduced oxygen can affect heart and lung function and limit oxygen reaching the brain. Back sleeping avoids all of these risks.
Side sleeping is not a safe alternative. The position is unstable, and babies placed on their sides frequently roll onto their stomachs. Some research suggests that a baby who usually sleeps on their back but is placed on their stomach or side, even for a single nap, faces dramatically higher SIDS risk, up to 45 times higher in certain studies. Consistency matters: every sleep, every time, on the back.
A common worry is that back-sleeping babies will choke on spit-up. The anatomy actually works in their favor. When a baby is on their back, the windpipe sits above the esophagus, so any fluid from the stomach has to travel upward against gravity to reach the airway. Babies naturally swallow or cough up fluids to keep their airway clear. Even babies diagnosed with gastroesophageal reflux should sleep on their backs.
What Belongs in the Crib
The only things that should be in a crib are the baby, a firm mattress, and a fitted sheet. That’s it. No pillows, blankets, stuffed animals, bumper pads, loveys, or positioning devices. Each of these items has been linked to deaths from suffocation, strangulation, or entrapment. Crib bumpers alone have caused enough injuries and fatalities to prompt specific warnings from safety organizations.
Weighted blankets and weighted swaddles are also unsafe. Non-fitted sheets, even lightweight ones that are tucked in, pose a suffocation risk. Adding any soft layer to the mattress, whether a blanket, quilt, or sheepskin, measurably increases the softness of the sleep surface and raises the danger. If you’re worried about your baby being cold, a wearable blanket or sleep sack is a safer option than loose bedding.
Choosing a Firm Sleep Surface
A firm, flat mattress is essential. Research into infant sleep surfaces has found a surprisingly wide range of softness among products marketed for babies, with some infant mattresses testing as soft as adult mattresses. There’s no official national standard defining exactly how firm is firm enough, so use a simple test: press your hand into the mattress and release. It should snap back immediately and not conform to the shape of your hand. If it leaves an impression, it’s too soft.
Soft surfaces like couches, waterbeds, memory foam pads, air mattresses, and pillow-top adult mattresses are never safe for infant sleep. About a quarter of sudden unexpected infant deaths involve unintentional suffocation, and soft bedding on soft surfaces is a major contributing factor.
Room Sharing Without Bed Sharing
Place the crib or bassinet in your bedroom, close to your bed, for at least the first six months. The American Academy of Pediatrics recommends room sharing (but not bed sharing) ideally through the first year. Infants who sleep in a separate room are roughly 3 to 12 times more likely to die suddenly and unexpectedly compared to those who room share. The risk of sleep-related death is highest in the first six months, making this period especially important.
The baby needs their own sleep surface. Falling asleep with a baby on a couch, recliner, or adult bed creates one of the highest-risk scenarios for suffocation, even if you don’t intend to fall asleep there.
Crib Safety Basics
Crib slats should be no more than 2⅜ inches apart, roughly the width of a soda can. Any wider and a baby’s body could slip through. Check that no slats are missing or cracked. Corner posts should not extend more than 1/16 of an inch above the end panels, because taller posts can catch on clothing and create a strangulation hazard. If you’re using a secondhand crib, verify it meets current safety standards, as older models may have been recalled.
Swaddling Safely
Swaddling can help newborns sleep more comfortably, but it has a firm expiration date. Once your baby shows any signs of rolling, swaddling must stop. Most babies reach this milestone between 3 and 4 months. The sign to watch for is your baby getting their body up onto one shoulder, which indicates they’re developing the strength to roll. A swaddled baby who rolls onto their stomach has no way to use their arms to push up or reposition, which is extremely dangerous.
If your baby is under 3 months and not yet showing any rolling signs, swaddling is still fine. Once you transition out of the swaddle, a sleep sack with arm openings is a good alternative to keep your baby warm.
Preventing Flat Spots on the Head
Back sleeping can sometimes lead to a flat spot on the back of a baby’s head. A simple strategy prevents this: alternate which end of the crib you place your baby’s head each day. One day, lay them with their head at the top of the crib. The next day, position them with their head at the foot. Babies tend to turn their heads to look out toward the room, so alternating their orientation naturally shifts which side of the head bears the most pressure. Placing a mobile on the room-facing side of the crib encourages your baby to turn in that direction. Plenty of supervised tummy time while your baby is awake also helps strengthen neck muscles and relieve pressure on the back of the skull.
Room Temperature and Overheating
Keep the room between 68°F and 72°F (20°C to 22°C). Overheating is an independent risk factor for SIDS, so erring on the cooler side is better than overdressing your baby. A good rule of thumb: dress your baby in one layer more than you’d wear comfortably in the same room.
Signs of overheating include skin that feels hot to the touch (especially on the neck, back, or underarms), sweating, heat rash, rapid breathing, or unusual fussiness. Some overheated babies become unusually quiet or lethargic rather than fussy. If you notice any of these signs, remove a layer of clothing or lower the room temperature.
Pacifier Use During Sleep
Offering a pacifier at bedtime and naptime is associated with a lower risk of SIDS. The protective mechanism isn’t fully understood, but it may involve improved breathing control or keeping the airway more open during sleep. If you’re breastfeeding, waiting until nursing is well established (typically a few weeks) before introducing a pacifier is reasonable. If the pacifier falls out after your baby falls asleep, there’s no need to put it back in.
Once Your Baby Can Roll
Continue placing your baby on their back at the start of every sleep. Once babies develop the strength to roll both ways on their own, typically around 4 to 6 months, you don’t need to reposition them if they roll during sleep. The key is that you always start them on their back. By this point, the swaddle should already be gone so their arms are free to adjust their position.