The ideal approach is to keep the room between 68°F and 72°F and dress your baby in a single layer plus a lightweight sleep sack. Babies lose excess heat through their heads and extremities, so getting the clothing right matters more than you might expect. Too many layers in an air-conditioned room can be just as risky as too few.
Why Room Temperature Matters So Much
Babies regulate their body temperature poorly compared to adults. Their sweat response is only about one-third as effective as an adult’s, despite having a higher density of sweat glands. This means they can overheat quickly when over-dressed, and they also lose heat faster when under-dressed. That imbalance doesn’t fully resolve until around age two.
Overheating during sleep is a known risk factor for SIDS. Research published in ScienceDirect found that months with extreme temperature swings, where babies might be dressed for one temperature and exposed to another, were significantly associated with increased SIDS risk. High humidity compounded the danger. Air conditioning actually helps by keeping the temperature stable, but only if you dress your baby appropriately for the cooler environment it creates.
The widely recommended target is 68°F to 72°F (20°C to 22°C) for a baby’s sleep space. If your AC keeps the room in that range, you’re in the sweet spot.
What to Dress Baby In at Each Temperature
A system called TOG ratings makes this straightforward. TOG measures how much warmth a sleep sack or blanket provides, with higher numbers meaning more insulation. Here’s what works at common AC settings:
- 68°F to 72°F (most AC settings): A short-sleeve or long-sleeve cotton onesie under a 1.0 TOG sleep sack. A 0.5 TOG sack works here too if your baby tends to run warm.
- 72°F to 75°F (warmer AC or mild cooling): A short-sleeve onesie with a 0.5 TOG sleep sack, or just a onesie alone.
- 75°F and above (minimal AC): A short-sleeve onesie or just a diaper with a 0.2 TOG sleep sack.
- Below 68°F (aggressive AC): A long-sleeve onesie or footed pajamas under a 2.5 TOG sleep sack.
If you don’t have a sleep sack with a TOG rating on the label, use this rule of thumb: a single layer of muslin or thin cotton is roughly 0.5 TOG, and a quilted or fleece-lined sack is closer to 2.5.
How to Check if Baby Is Comfortable
Don’t go by your baby’s hands or feet, which naturally feel cooler. Instead, touch the back of their neck or their chest. The skin should feel warm and dry. If it’s hot or damp, your baby is overdressed. If it feels cool to the touch, add a layer.
Signs of overheating include flushed cheeks, sweaty hair, rapid breathing, and restlessness. Signs your baby is too cold include fussiness, cool skin on the torso, and mottled or bluish-looking extremities. In an air-conditioned room, most parents err on the side of overdressing, so check for warmth first.
Choosing the Right Fabrics
Cotton is the go-to for infant sleepwear because it breathes well and wicks moisture. Bamboo-blend fabrics work similarly and feel softer against sensitive skin. Both are good choices for air-conditioned rooms.
Some baby sleepwear now uses phase-change materials, originally developed from NASA spacesuit research, that absorb heat when your baby gets warm and release it when they cool down. These fabrics help smooth out temperature fluctuations during the night, which can be particularly useful if your AC cycles on and off.
Avoid polyester and synthetic fleece as a base layer against the skin. They trap heat and moisture, which can cause your baby to overheat even in a cool room. If you use a fleece-lined sleep sack, make sure the layer underneath is breathable cotton or bamboo.
Where to Place the Crib
Never position the crib directly under an AC vent or in the path of a window unit’s airflow. Cold air blowing directly on a sleeping baby can drop their skin temperature quickly, even if the room’s overall temperature is fine. Place the crib against an interior wall where airflow is indirect and the temperature stays even.
If you can’t avoid placing the crib near a vent, use a vent deflector to redirect the airflow toward the ceiling. You can also partially close the vent in the nursery and adjust the thermostat to compensate.
Managing Humidity in AC Rooms
Air conditioning pulls moisture from the air, and rooms can get dry enough to irritate a baby’s skin and airways. Boston Children’s Hospital recommends keeping indoor humidity between 35% and 50%. Below that range, babies are more likely to develop dry skin, nosebleeds, and difficulty breathing.
A simple hygrometer (available for a few dollars at any hardware store) lets you monitor the level. If humidity drops below 35%, a cool-mist humidifier in the nursery can bring it back into range. Clean the humidifier regularly to prevent mold growth.
What Not to Use
The AAP specifically advises against putting a hat on your baby for indoor sleep. Babies release a significant portion of excess heat through their heads, and a hat blocks that cooling mechanism. This applies even if the room feels cool to you.
Loose blankets, pillows, and stuffed animals don’t belong in the crib regardless of temperature. Sleep sacks exist precisely to replace blankets safely. Swaddles are appropriate for newborns who haven’t started rolling, but once your baby shows signs of rolling over, switch to a sleep sack with arms free.
Socks and mittens are generally unnecessary if you’re using a footed sleep sack or if the room is in the 68°F to 72°F range. Cool hands and feet are normal for babies and don’t indicate that they’re cold.
Adjusting for Newborns vs. Older Babies
Newborns under about three months have the hardest time regulating temperature. Their small body mass loses heat quickly, and their sweat response is immature. For newborns in air-conditioned rooms, lean toward the warmer end of the clothing spectrum: a long-sleeve onesie with a 1.0 TOG sleep sack at 70°F, for example, rather than a short-sleeve onesie alone.
By six months, most babies are better at maintaining their core temperature, and you can follow the standard TOG guidelines more loosely. Older babies also move around more during sleep, which generates additional body heat. If your eight-month-old kicks and rolls all night, they may need less insulation than the chart suggests.