Babies should always sleep on their backs, on a firm and flat mattress, with nothing else in the crib. That’s the core rule, and everything else builds from it. A bare crib with a snug-fitting mattress and a fitted sheet is the safest sleep setup for an infant, from the first night home through the first year of life.
Why Back Sleeping Matters
When a baby lies on their back, the windpipe sits above the esophagus (the food tube). If your baby spits up, gravity pulls that liquid down to the lowest point, away from the airway. Flip a baby onto their stomach and the anatomy reverses: the windpipe is now below the food tube, making it easier for spit-up to flow into the lungs. This is why back sleeping is so strongly linked to lower rates of SIDS and why every major health organization recommends it for every sleep, including naps.
Some parents worry that back sleeping increases the risk of choking. It actually does the opposite. Healthy babies have reflexes that clear their airways, and the physics of back sleeping work in their favor. Place your baby on their back for every single sleep until they can consistently roll both ways on their own. Once a baby can roll freely in both directions, you don’t need to reposition them if they shift during the night, but you should still always place them down on their back to start.
Setting Up the Crib
The mattress is the most important part. It should be firm and flat, fitting snugly inside the crib frame with no gaps around the edges. If you can fit more than two fingers between the mattress and the crib side, the mattress is too small. A standard full-size crib measures roughly 52⅜ inches by 28 inches, and mattresses made for that size should lock in tightly.
Crib slats should be spaced no more than 2⅜ inches apart, about the width of a soda can. Wider gaps create a risk of a baby’s body or head becoming trapped. Check that no slats are missing or cracked. If you’re using a secondhand crib, verify it meets current safety standards, as older cribs with drop sides were recalled years ago and should never be used.
The only thing on the mattress should be a single fitted sheet designed for that specific mattress size. Nothing else belongs in the crib: no blankets, no pillows, no stuffed animals, no bumper pads, no sleep positioners.
What to Keep Out of the Crib
Babies who sleep on or near soft objects are significantly more likely to die from SIDS or suffocation. That includes items that seem harmless or even protective. Crib bumpers, despite being widely sold for years, are linked to deaths from suffocation, entrapment, and strangulation. There is no evidence they prevent injuries, and several states have banned their sale.
Loose blankets, quilts, pillows, and stuffed toys all pose the same risk. A baby who shifts during sleep can end up face-down against a soft surface without the strength or coordination to move away. Weighted blankets and weighted swaddles are also unsafe for infants. If you’re concerned about your baby being cold, a wearable blanket or sleep sack is a safe alternative. These keep your baby warm without any loose fabric that could cover the face.
Swaddling Safely
Swaddling can help calm a newborn, but it comes with a firm expiration date. You need to stop swaddling as soon as your baby shows any sign of rolling over, which can happen as early as 8 weeks, though it more commonly occurs between 2 and 6 months. A swaddled baby who rolls onto their stomach cannot use their arms to push up or reposition, creating a serious suffocation risk.
While swaddling, keep the wrap snug around the arms but loose around the hips to allow healthy leg movement. The swaddle should never cover the baby’s face. Once rolling signs appear, transition to a sleep sack with arms free.
Room Temperature and Overheating
The recommended room temperature for a sleeping baby is 61 to 68°F (16 to 20°C). Overheating is an independent risk factor for SIDS, so cooler is generally better than warmer. Dress your baby in one layer more than you’d wear comfortably in the same room. A onesie under a lightweight sleep sack is usually enough.
Signs of overheating include sweating, damp hair, flushed cheeks, heat rash, and rapid breathing. Feel your baby’s chest or the back of their neck to check. Hands and feet often feel cool on infants, so they’re not a reliable gauge. Fans can help with air circulation in warmer months and have been associated with reduced SIDS risk in some studies.
Room Sharing Without Bed Sharing
The American Academy of Pediatrics recommends keeping your baby’s crib in your bedroom for at least the first six months, ideally the first year. Room sharing, where the baby sleeps on a separate surface near your bed, reduces the risk of SIDS. You can hear and respond to your baby quickly without the dangers of sharing a sleep surface.
Bed sharing is a different matter entirely. Adult mattresses are too soft for infants, and pillows, blankets, and the sleeping adult all pose suffocation and overlay risks. Research also shows that room sharing itself makes bed sharing more likely, with parents roughly four times more likely to bring their baby into bed at both 4 and 9 months when sharing a room. Being aware of this tendency can help you resist the temptation on exhausting nights. If you’re feeding your baby in bed, put them back in the crib before you fall asleep.
Pacifiers and SIDS Reduction
Offering a pacifier at bedtime and naptime is associated with a lower risk of SIDS. The protective mechanism isn’t fully understood, but researchers believe pacifiers may improve an infant’s automatic control of breathing or help keep the airway open during sleep. There’s also a theory that the pacifier’s bulk makes accidental rolling less likely.
If you’re breastfeeding, wait until nursing is well established before introducing a pacifier, typically around 3 to 4 weeks. If the pacifier falls out after your baby is asleep, you don’t need to put it back in. And if your baby refuses it, don’t force it.
Products That Are Not Safe for Sleep
Car seats, swings, bouncers, rockers, and any product that places a baby at an incline greater than 10 degrees are not designed for sleep. In a seated or semi-reclined position, a baby’s head can tip forward and block their airway. This is called positional asphyxia, and young babies lack the muscle control to correct it on their own.
If your baby falls asleep in a swing or car seat, move them to a flat, firm crib as soon as possible. Inclined sleepers were once marketed specifically for overnight use, but after dozens of infant deaths, they were recalled and the CPSC now prohibits inclined sleep products with angles over 10 degrees. The only safe surfaces for unsupervised infant sleep are a crib, bassinet, or play yard that meets current federal safety standards, with a firm, flat mattress and nothing else inside.