Too hot or too cold to sleep well?

The Best Temperature for Sleep: What the Studies Show

Reviewed 2026-11-02 · 7 sources · By Anthony Falcone

The short answer: There is no single perfect number, but cool to moderate wins. In the best home study we found, older adults slept most efficiently with the bedroom at 20–25 °C, and sleep got worse as it warmed above that. With normal bedding a cool room disturbs sleep far less than a hot one, so keep the room cool and the bed warm.^1,2

Before you start

Loud snoring, pauses in breathing or gasping at night, or feeling sleepy all day are reasons to see a doctor, not to change the thermostat. Large studies in a 2026 review linked higher temperatures with worse sleep apnoea.⁴
If you are older or have heart disease, ask your doctor how to stay safe in heatwaves. The studies behind this guide found older adults, and people with chronic illness, more affected by hot nights.^2,4
If you take regular medicines, ask your pharmacist whether any of them change how your body copes with heat.
Before trying a hot bath before bed, check with your doctor if you have heart disease or low blood pressure, or are pregnant. Night sweats in a cool room, hot flushes that keep waking you, or poor sleep that lasts for months are also reasons to see a doctor.

20–25 °C bedroom temperature at which older adults slept most efficiently and restfully at home (observational, 10,903 nights)¹
60 min less sleep predicted when the bedroom warmed from 22 to 30 °C, in the same study¹
13–23 °C room temperatures that made no difference to sleep stages in lab studies with bedding and nightclothes²
32–34 °C the usual temperature under the covers when people sleep normally²
40–42.5 °C bath or shower water, 1–2 hours before bed, linked with better sleep in a meta-analysis⁵
16.3 vs 8.8 times woken in a night without and with bed socks in a 23 °C room (6 young men)⁶

What is the best temperature for sleep?

The best real-world data we found come from Boston, where 50 adults aged 65 or over (79 on average) had a temperature sensor in the bedroom and wore a sleep-tracking ring for up to 12 months: 10,903 nights in all. Sleep was most efficient and restful when the bedroom was at 20–25 °C. Warming from 22 to 30 °C went with about a 10% drop in sleep efficiency and 60 minutes less predicted sleep; cooling from 22 to 14 °C went with about a 5% drop.¹

That study is observational: people set their own heating and cooling, so it shows what went together, not cause and effect. It also found large differences between people, with the link between temperature and sleep running in opposite directions for different participants.¹

Lab studies explain why one number is hard to give. For lightly dressed people with no covers, rooms warmer or cooler than about 29 °C (the thermally neutral point) brought more waking and less deep and REM sleep. With bedding and nightclothes, though, studies found no difference in sleep stages between 13 and 23 °C, or between 3 and 17 °C, and older adults' sleep, measured with a wrist sensor, did not differ between 9 and 20 °C.²

Recommended ranges vary for the same reason: they depend on what people wear and sleep under. The authors of a bed-sock trial cite earlier work proposing 25–27 °C, and the authors of a 2025 cooling trial quote 17–28 °C as the range assumed for bedroom design.^6,7

Why a cool room helps you sleep

Your core temperature falls at night, and sleep comes most easily while it is falling. The body sheds that heat through the skin, especially the hands and feet, which is why warming the feet has been shown to shorten the time it takes to fall asleep. A hot room slows that heat loss and keeps the core temperature from dropping, which disturbs the first part of the night most.²

What counts is the room and the bed together. When people sleep normally, the air under the covers is usually about 32–34 °C with 40–60% humidity. Covers keep that pocket of warm air steady even when the room is cold, which is why a cool room with a warm bed works.²

Is it worse to sleep too hot or too cold?

Too hot. In real-life conditions, with covers and nightclothes, heat disturbs sleep in young and older adults while cold does not change sleep stages. Heat brings more waking and less deep and REM sleep, mostly early in the night, and in one experiment sleep had still not adapted after 5 days of heat.²

A 2024 systematic review of studies that measured sleep in everyday life reached the same conclusion: higher outdoor or indoor temperatures generally went with worse and shorter sleep, more so in the hottest months, in vulnerable groups and in the warmest regions. The reviewers found little evidence that people adapt quickly.³

Cold is not harmless just because you sleep through it. In the lab it changed heart-rhythm measures during sleep without changing sleep stages, and the review's authors advise keeping a bedroom above 10 °C in winter.²

The best temperature for sleep in summer

Humidity makes heat worse: humid heat brings even more waking and less deep and REM sleep than dry heat. In the Boston home study, sleep efficiency was best at about 50% humidity, although humidity mattered less than temperature.^2,1

Moving air and air conditioning help. In a lab study of 16 older adults described in a 2026 review, a 30 °C room cut sleep by 26.3 minutes and sleep efficiency by 5.5% compared with 27 °C, with 27 minutes more time awake; adding air movement at 30 °C won back 10.3 minutes of deep sleep and 3.7 minutes of REM sleep. In another study, frequent air conditioning use reduced the 2% drop in sleep efficiency per degree seen in people without it.⁴

If you can only cool part of the night, cool the start: heat early in the night is the most disruptive, so the authors of a review suggest using air conditioning then. If it runs later in the night, dry off any sweat and change into dry clothes so you don't get chilled.²

How you cool may matter too. In a small trial, 7 women slept in a room held at 26 °C by two systems in turn. With radiant ceiling cooling the air was drier (about 60% humidity against 80%) and less draughty than with an ordinary air conditioner, and they fell asleep faster, slept more efficiently and felt more refreshed. The trial was funded by a company several authors work for, and it can't separate the effect of humidity from the type of cooling.⁷

Warm bath, warm feet: heat that helps

Warming up before bed is different from sleeping in a warm room. A 2019 meta-analysis found 17 studies of a warm bath or shower before bed and pooled 13 of them. Water at 40–42.5 °C was linked with better self-rated sleep quality and sleep efficiency, and taken 1–2 hours before bed, for as little as 10 minutes, with falling asleep faster. The authors think it works by sending blood to the hands and feet so the body sheds more heat afterwards, and say the best timing and length still need research.⁵

Warm feet during the night may help too. In a small trial, 6 young men slept in a 23 °C lab with and without loose bed socks, in random order. With socks they fell asleep 7.5 minutes sooner, slept 32 minutes longer and woke 8.8 times instead of 16.3, and sleep efficiency was 93.8% against 86.2%. Their core temperature did not differ between the two nights, and they did not rate their sleep any better the next morning.⁶

Best temperature for sleep for women and older adults

We found no study that sets a different ideal temperature for women. In large studies of hot nights summarised in a 2026 review, women were among the groups whose sleep suffered most, along with older adults and people on lower incomes; one small study in care homes found the opposite, with men sleeping worse than women.⁴

Older adults have the clearest reason to keep the bedroom from getting hot. Ageing reduces skin blood flow and sweating, so the body loses heat less well; even mild heat increases waking and cuts REM sleep in older people and doubles how much they sweat overnight. The 20–25 °C range above came from adults aged 65 or over.^4,2,1

What to do with this

If you can, keep the bedroom around 20–25 °C, and above all stop it climbing past 25 °C, the point beyond which sleep got worse in the home study.¹
Cooler is fine if your bed is warm: with normal bedding, rooms from 13 to 23 °C made no difference to sleep stages in the lab. In winter, keep the bedroom above 10 °C.²
On hot nights, use a fan or air conditioning; if you can only cool part of the night, cool the first part.^4,2
Keep humidity moderate: about 50% went with the best sleep efficiency at home, and humid heat is the hardest on sleep.^1,2
To fall asleep faster, try a warm bath or shower at 40–42.5 °C, 1–2 hours before bed, for at least 10 minutes, and wear bed socks if your feet get cold.^5,6

How sure is this?

The best home data are observational: 50 older adults in one US city with a relatively high standard of living, measured with a consumer sleep ring rather than a sleep lab. People chose their own temperatures, so it can't prove that temperature caused the differences.¹
The trials are tiny: 6 young men in the bed-sock trial and 7 women in the cooling trial. The cooling trial was funded by a company several authors work for, and two authors hold stakes in the company that made its sleep-recording device.^6,7
Much of the evidence on heat comes from studies of hot weather, often in older adults. The 2026 review was a scoping review, which does not rate study quality or pool results, so we report its numbers as described there.^4,3
We could read only the summary of the bath meta-analysis, so we give no effect size in minutes. The bed-sock trial's summary says awakenings were "7.5 times smaller", but its table shows 16.3 against 8.8; we used the table.^5,6

Common questions

What is the best room temperature for sleep?

Cool to moderate. In a home study of older adults, sleep was most efficient with the bedroom at 20–25 °C, and with warm bedding even cooler rooms did not disturb sleep stages in the lab.^1,2

Is 18 degrees too cold to sleep?

Not if your bedding keeps you warm. In lab studies with covers and nightclothes, sleep stages did not differ between 13 and 23 °C.²

What is the best temperature for sleep in summer?

Try to keep the bedroom from going above about 25 °C; above that, older adults in a home study slept less efficiently. Fans and air conditioning helped in studies of hot nights.^1,4

Is it better to sleep hot or cold?

Slightly cool, under warm covers. With normal bedding, heat disturbed sleep while cold did not change sleep stages, though the review's authors still advise keeping a bedroom above 10 °C in winter.²

What is the best temperature for sleep for women?

We found no study that sets a separate ideal for women. Large studies found women among the groups whose sleep suffered most on hot nights, so keeping the bedroom cool matters at least as much.⁴

Does a warm shower before bed help you sleep?

It may. In a meta-analysis, a bath or shower at 40–42.5 °C taken 1–2 hours before bed, for as little as 10 minutes, was linked with falling asleep faster.⁵

Sources

Baniassadi A, Manor B, Yu W, Travison T, Lipsitz L. Nighttime ambient temperature and sleep in community-dwelling older adults. Science of the Total Environment, 2023. Survey / forum study. doi.org/10.1016/j.scitotenv.2023.165623
Okamoto-Mizuno K, Mizuno K. Effects of thermal environment on sleep and circadian rhythm. Journal of Physiological Anthropology, 2012. Review. doi.org/10.1186/1880-6805-31-14
Chevance G, Minor K, Vielma C, Campi E, O'Callaghan-Gordo C, Basagaña X, Ballester J, Bernard P. A systematic review of ambient heat and sleep in a warming climate. Sleep Medicine Reviews, 2024. Review. doi.org/10.1016/j.smrv.2024.101915
Krčum J, Ezgin N, Šutulović N, Rajković N, Djurić E, Mladenović D, Vesković M, Cetin AE, Rašić-Marković A, Stanojlović O, Hrnčić D. Effects of Heatwaves and Tropical Nights on Sleep in Middle-Aged and Older Adults: A Scoping Review. Clocks & Sleep, 2026. Review. doi.org/10.3390/clockssleep8030037
Haghayegh S, Khoshnevis S, Smolensky MH, Diller KR, Castriotta RJ. Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis. Sleep Medicine Reviews, 2019. Meta-analysis. doi.org/10.1016/j.smrv.2019.04.008
Ko Y, Lee JY. Effects of feet warming using bed socks on sleep quality and thermoregulatory responses in a cool environment. Journal of Physiological Anthropology, 2018. Randomised trial. doi.org/10.1186/s40101-018-0172-z
Park I, Cui Y, Kawana F, Tominaga M, Miyamura R, Yamagishi H, Okado M, Miyamura M, Nakamura S, Tanigawa C, Kokubo T, Yanagisawa M, Tokuyama K. Subjective and objective quality of sleep with radiant or convection cooling systems: a randomized, cross-over trial. Scientific Reports, 2025. Randomised trial. doi.org/10.1038/s41598-025-19163-8

The Deep Sleep Protocol starts with the sleep apnoea and insomnia signs that need a doctor, then gives you the CBT-I rules sleep clinics use (a fixed wake time and stimulus control), a two-week sleep diary, an evening light and screen plan, and the honest evidence on magnesium and melatonin. If hot flushes are what wake you, the Perimenopause Protocol covers what the evidence supports for them, CBT for insomnia, and the red flags that mean seeing a doctor. Deep Sleep Protocol · The Perimenopause Protocol