What’s the best temperature to sleep at?

Key takeaways

• A 2019 review of sleep and temperature puts the best bedroom range at about 66 to 70°F (19 to 21°C).

• In a study of older adults sleeping at home, sleep was most efficient between 68 and 77°F (20 and 25°C).

• With normal bedding, heat disrupts sleep more than cold does, because blankets and clothing buffer a cool room.

• Too much heat cuts into deep sleep and REM sleep and adds wake time, and in one study the effect hadn’t faded after five days of continuous heat.

• The NHS advises keeping a baby’s room at about 61 to 68°F (16 to 20°C).

How cool a bedroom should be

There’s no single perfect number, but the research clusters in a fairly narrow band. A 2019 review on the temperature dependence of sleep describes optimal room temperatures of roughly 66 to 70°F (19 to 21°C). In those rooms, people try to keep the air right next to their skin, under the covers, between about 88 and 95°F (31 and 35°C).

That second figure is the one the body cares about. Bedding, sleepwear, and the mattress all trap warmth, so a room that feels chilly while you’re up can be comfortable once you’re in bed. The goal is a room cool enough that the bed doesn’t overheat, and not so cold that you can’t stay warm under the covers.

Why the body cools down to fall asleep

Falling asleep and losing heat go together. Core body temperature drops in the evening, and NREM sleep is most likely to start when that temperature is falling fastest, according to the 2019 review. The lowest point usually comes about two hours after lights out.

To get rid of heat, the body widens the blood vessels in the hands and feet, which releases warmth through the skin. This shift can begin up to two hours before sleep, and it’s a good predictor of when someone will drop off. Warming the skin helps the same process along. A 2012 review of thermal environment and sleep notes that warming the feet has been shown to shorten the time it takes to fall asleep.

A warm room works against all of this. The body can’t shed heat as easily, so the drop in core temperature that comes with sleep is harder to reach.

What happens when the room is too warm

For sleep itself, heat is the bigger problem. The 2012 review reports that when people sleep with bedding and clothes, as in real life, heat exposure increases wake time and reduces both slow-wave (deep) sleep and REM sleep. Most of that damage lands in the first part of the night.

People don’t seem to get used to it, either. In one study the review cites, sleep disruption from heat hadn’t eased after five days of continuous day-and-night heat. Humid heat is worse than dry heat, most likely because sweat can’t evaporate and the skin stays wet.

The home study of older adults put numbers on it. Researchers tracking 50 people aged 65 and over for a combined 10,903 nights found that a rise from 72°F to 86°F (22°C to 30°C) went with about a 10% drop in sleep efficiency and about 60 fewer minutes of sleep.

What happens when the room is too cold

Cold is easier to manage, because blankets do most of the work. The 2012 review describes a study where sleep didn’t differ significantly across room temperatures from 55 to 73°F (13 to 23°C) with normal bedding, since the temperature inside the bed stayed fairly steady. In older adults, sleep measured by a movement monitor didn’t differ significantly between 48°F and 68°F (9°C and 20°C).

Cold isn’t entirely harmless. It can affect the heart’s responses during sleep without changing sleep stages, and when cold does disturb sleep, it tends to hit the second half of the night, when REM is most common. In the older-adult study, a drop from 72°F to 57°F (22°C to 14°C) went with about a 5% fall in sleep efficiency, half the effect of the same-sized rise in heat.

The temperature inside the bed

The space between your body and the covers has its own climate. When people sleep well, the 2012 review reports, this bed climate usually sits around 90 to 93°F (32 to 34°C), with relative humidity between 40% and 60%.

That’s why the same room can suit one person and not another. What counts is how warm it gets under each person’s own covers, and bedding can hold that bed climate fairly steady even as the room temperature changes.

Where humidity comes in

Humidity matters mostly when it’s hot. Moist air likely keeps sweat from evaporating, which makes heat harder to shed and disturbs sleep more than dry heat at the same temperature. In the older-adult study, sleep efficiency peaked at around 50% relative humidity in the bedroom, though humidity had a smaller effect than temperature.

Temperature figures from the research

How the advice changes for older adults and babies

Older adults appear to be more sensitive to heat. In the 2012 review, even mild heat increased wake time and reduced REM in older people, and it doubled their whole-body sweat loss. The home study also found wide differences between individuals, so a range that suits one older adult won’t necessarily suit another.

For babies, overheating is a concern because it can raise the risk of sudden infant death syndrome (SIDS). The NHS advises keeping a baby’s room at about 61 to 68°F (16 to 20°C) and checking the baby’s temperature by feeling the chest or the back of the neck. Cool hands and feet are normal.

Frequently asked questions

Is 72°F too warm to sleep?

It’s a little above the 66 to 70°F range in the 2019 review, but within the 68 to 77°F range where older adults slept most efficiently in the home study. Whether it feels too warm depends a lot on bedding and sleepwear, since those set the temperature right next to the skin.

Is it better to sleep too cold or too warm?

Slightly cool is easier to fix. Extra blankets can keep the bed comfortable in a cool room, and studies with normal bedding found little change in sleep over a wide range of cool temperatures. Heat cuts into deep sleep and REM.

Why are my hands and feet warm when I’m falling asleep?

Warm hands and feet are part of how the body cools down. Blood vessels near the skin of the hands and feet widen to release heat, and this shift often starts before sleep and helps predict when it begins.

What temperature should a baby’s room be?

The NHS advises about 61 to 68°F (16 to 20°C), with a room thermometer to check, and warns against putting a baby to sleep next to a radiator or heater or in direct sunlight.