A newborn should sleep on a firm, flat mattress inside a safety-approved crib or bassinet, wearing one layer of fitted sleepwear or a lightweight sleep sack, with nothing else in the sleep space. No blankets, no pillows, no stuffed animals, no bumper pads. That bare setup is the safest arrangement for every sleep, including naps.
The Sleep Surface
The foundation of safe newborn sleep is a firm, flat mattress that fits snugly inside a full-size crib or bassinet. “Firm” in this context means firmer than you’d probably choose for yourself. Crib mattresses sold in the U.S. must pass a federally regulated firmness test where a weighted arm presses into the surface and cannot make contact with the mattress at all. If it gives even slightly, it fails. That level of firmness prevents a baby’s face from sinking into the surface, which reduces suffocation risk.
The mattress also needs to fit tightly inside the crib frame. For full-size cribs, the gap between the mattress edge and the crib side should be no more than about 1.5 inches. For smaller bassinets and non-full-size cribs, that gap shrinks to 1 inch. If you can fit more than two fingers between the mattress and the side, the mattress is too small for that crib. Cover it with a single fitted sheet and nothing else.
What Goes Inside the Crib
Your baby and the fitted sheet. That’s it.
Items that should never be in the sleep area include loose blankets, pillows, crib bumper pads, stuffed animals, soft toys, and sleep positioners. The FDA specifically warns against infant sleep positioners due to the risk of serious harm. Crib tents are also on the list of products to avoid. Even items marketed with claims about preventing SIDS, like special pillows or wedges, are not recommended and can actually increase risk.
This applies to every sleep, day and night. It’s tempting to add a blanket during a nap on a cool afternoon, but the same rules hold regardless of when your baby is sleeping.
Where to Put the Crib
Keep the crib or bassinet in your bedroom for at least the first six months. Room-sharing (not bed-sharing) lets you monitor your baby during sleep and respond quickly to feeding cues or any signs of distress. The key distinction: the baby sleeps on their own separate surface, not in your bed.
What Your Newborn Should Wear to Sleep
The goal with sleepwear is keeping your baby at a comfortable temperature without any loose fabric that could cover their face. A onesie or footed pajama works well as a base layer. In cooler rooms, a wearable blanket (also called a sleep sack) over that base layer is the safest way to add warmth, since it stays in place and can’t ride up over your baby’s face the way a blanket can.
Sleep sacks come with TOG ratings, which measure how much warmth the fabric traps. A 0.2 TOG sleep sack suits warm rooms (75 to 81°F). A 1.0 TOG works for the 68 to 75°F range. And a 1.5 TOG is appropriate when the room dips to 64 to 72°F. These numbers give you a starting point, but every baby runs a little warmer or cooler, so you’ll want to check by feeling the skin on their chest or the back of their neck.
One important rule: no hats indoors. Babies regulate their body temperature partly through their heads, and a hat traps that heat. Johns Hopkins Medicine specifically advises against using a hat on your baby indoors during sleep.
Swaddling: When It Works and When to Stop
Swaddling can help newborns sleep more soundly by reducing their startle reflex. A snug swaddle with arms wrapped in is generally fine for babies who are not yet showing any signs of rolling. The fabric should be tight enough to stay in place but loose enough around the hips to allow natural leg movement.
You need to stop swaddling as soon as your baby shows any sign of rolling over, which can happen as early as 8 weeks but more commonly occurs between 2 and 6 months. A swaddled baby who rolls onto their stomach cannot use their arms to reposition or clear their airway. The transition point is based on your baby’s development, not a fixed age. If they’re pushing up on their hands, arching their back, or rocking side to side, the swaddle needs to go. Transitioning to an arms-free sleep sack is the typical next step.
Room Temperature and Overheating
The ideal room temperature for a sleeping baby is 68 to 72°F (20 to 22°C). The Lullaby Trust, a UK-based infant safety organization, recommends a slightly wider range of 61 to 68°F (16 to 20°C) with appropriate layers. The important thing is that overheating raises the risk of SIDS more than being slightly cool does, so when in doubt, err on the side of one fewer layer rather than one more.
You typically don’t need to keep the heat running all night. If the room feels cool, adding a layer of clothing is safer and more effective than cranking the thermostat. On warm nights, a single-layer onesie or even just a diaper with a lightweight 0.2 TOG sack is enough. Opening a window or bedroom door can help with airflow if cooling the room is difficult.
Signs Your Baby Is Too Hot
Young newborns don’t sweat much, so you can’t rely on visible perspiration as your only cue. Instead, touch the skin on your baby’s chest or the back of their neck. If it feels hot or clammy, they’re overdressed. Other signs of overheating include flushed or red skin, damp hair, unusual fussiness or restlessness, and seeming overly tired or sluggish. A baby who feels hot to the touch but isn’t running a fever is likely overheated from their environment or clothing rather than illness.
Always on Their Back
Place your baby on their back for every sleep, both naps and nighttime. Back sleeping is the single most effective way to reduce the risk of SIDS. This applies even if your baby seems to prefer sleeping on their side or stomach. Once babies can roll both ways on their own (usually around 4 to 6 months), you don’t need to reposition them if they roll during sleep, but you should still place them on their back at the start.