Always lay your baby on their back, on a firm and flat mattress, with nothing else in the crib. That single practice, promoted through the “Back to Sleep” campaign starting in 1994, cut the rate of sudden infant death syndrome (SIDS) in the United States by more than 50%. Every sleep time, naps included, should start with your baby face-up on a bare crib surface covered only by a fitted sheet.
Back, Every Single Time
Place your baby squarely on their back, centered on the mattress. Not on their side, not on their stomach. Side-sleeping can seem like a compromise, but babies placed on their sides easily roll onto their stomachs, which increases suffocation risk. The back position keeps the airway clear and is the safest orientation for every nap and every night of sleep through the first year.
Most babies start rolling on their own around 4 to 6 months. If your baby rolls onto their stomach independently during sleep, you do not need to flip them back over. What matters is that you always start them on their back. By the time a baby can roll both ways, they generally have the head and neck control to keep their airway open. Just make sure the crib is completely free of soft bedding so there’s nothing to obstruct their face.
What Belongs in the Crib (and What Doesn’t)
The crib should contain a firm, tight-fitting mattress and a fitted sheet. That’s it. No pillows, blankets, stuffed animals, bumper pads, or loose fabric of any kind. These items increase the risk of entrapment, suffocation, and strangulation. Products that attach to the crib, like toys or fabric organizers, should also stay out.
If you’re worried about your baby getting cold, use a wearable blanket or sleep sack instead of a loose blanket. These are sleeveless garments worn over pajamas that provide warmth without any loose material in the crib. The AAP specifically recommends layers of clothing or a wearable blanket as the preferred way to keep a baby warm during sleep. Weighted swaddles and weighted sleep suits are not recommended because they can put too much pressure on a baby’s chest and lungs.
If you’re swaddling a younger baby, always place them on their back and monitor for any signs of rolling. Once your baby shows the first hints of rolling over, it’s time to stop swaddling and switch to a sleep sack with arms free.
The Crib Itself Matters
Before you lay your baby down, make sure the crib meets current safety standards. Slats should be no more than 2⅜ inches apart, roughly the width of a soda can. Any wider and an infant’s body could slip through. There should be no missing or cracked slats. The mattress should fit snugly against all four sides of the crib frame with no gaps where a baby could become trapped. If you can fit more than two fingers between the mattress edge and the crib wall, the mattress is too small.
Flat Surface Only, Even With Reflux
Parents of babies with reflux often feel tempted to elevate one end of the mattress, hoping gravity will reduce spit-up. This is understandable, but inclined sleep surfaces are genuinely dangerous. Inclined sleepers carry a fivefold increased risk of sudden unexpected infant death compared to a flat, firm surface. For babies 4 months and older, that risk jumps even higher, to roughly 10 times the baseline. The Rock ‘n Play sleeper alone was linked to over 100 infant deaths before being recalled, and federal law now bans the sale of any infant sleep product angled more than 10 degrees.
A pilot study looking specifically at babies with gastroesophageal reflux found that inclines between 10 and 28 degrees made no significant difference in regurgitation, drops in oxygen levels, or other reflux symptoms compared to lying flat on the back. In other words, elevating the mattress doesn’t reliably help with reflux and does introduce real danger. The AAP recommends flat, supine sleep for babies with reflux just as it does for all infants. If reflux is causing serious problems, talk to your pediatrician about feeding adjustments or other strategies that don’t involve changing sleep position.
Room Temperature and Dressing
Overheating is a known risk factor for SIDS. Aim to keep the room between 61°F and 68°F (16 to 20°C). A good rule of thumb: if the room feels comfortable to you in a T-shirt, it’s likely fine for a baby in a single layer of pajamas plus a lightweight sleep sack.
To check whether your baby is too warm, place your hand on their chest or back rather than their hands or feet. A baby’s hands and feet naturally run cooler than the rest of their body, so they’re not a reliable gauge. If your baby’s chest feels hot or sweaty, remove a layer. Signs of overheating include flushed skin, rapid breathing, damp hair, and restlessness.
Where to Place the Crib
Keep the crib or bassinet in your bedroom for at least the first six months. Room-sharing (not bed-sharing) makes nighttime feeding easier and lets you monitor your baby’s breathing and position without getting up. Place the crib away from windows, blinds with cords, and any hanging objects. Make sure no curtains, electrical cords, or monitor cables are within arm’s reach of the crib, as these pose strangulation hazards.
Putting It All Together
The routine itself is simple. Check that the crib is bare: firm mattress, fitted sheet, nothing else. Dress your baby in appropriate layers for the room temperature. Lay them gently on their back in the center of the mattress. Their feet can be near the bottom of the crib to discourage them from wriggling under any bedding (though ideally there’s no bedding to wriggle under). If they’re swaddled, confirm the swaddle is snug around the torso but loose at the hips to protect hip development, and that their face is completely clear.
Some babies fuss when placed on their backs. A consistent bedtime routine, a sleep sack that feels cozy, and a pacifier at sleep time can all help. What doesn’t help, and what isn’t safe, is placing them on their stomach “just this once” because they seem to sleep better that way. The risk doesn’t take a night off, and neither should the practice.