Body Temperature and Sleep: What the Research Says About Cooling Down

Sleep and body temperature are linked. Your core temperature follows a daily rhythm and falls when you sleep, and both a warm bath before bed and a hot bedroom have been studied. This guide sets out what five research papers (reviews) and two U.S. health agencies say, and where the evidence is thin.

It is not medical advice. If sleep trouble is persistent, talk to a healthcare provider.

The Short Answer

Core body temperature falls during sleep. A 2018 review says sleep in mammals is accompanied by a decrease in core body temperature, and that the body clock regulates the daily rhythms of both temperature and arousal.
Skin temperature away from the body’s core rises as you fall asleep. The same review says a sleep-related increase in distal skin temperature is a prominent feature of sleep onset in humans. It reflects reduced sympathetic tone to the blood vessels of the periphery, which lets heat leave through the skin.
A warm shower or bath before bed has been linked to better sleep. A 2019 meta-analysis found that water at 40 to 42.5 °C was associated with better self-rated sleep quality and sleep efficiency. When taken 1 to 2 hours before bed, even for 10 minutes, it was associated with falling asleep sooner. The authors say more research is needed.
Heat is linked to worse sleep. A 2024 systematic review found that higher outdoor or indoor temperatures are generally associated with degraded sleep quality and quantity.
No agency page we read gives a bedroom temperature. The CDC says to keep the bedroom at a cool temperature, and gives no number.

What Happens to Body Temperature at Night

The 2018 review, by Szymusiak, says the circadian clock in the hypothalamus regulates daily rhythms in core body temperature and arousal states, and that these rhythms are normally coupled. It names several contributors to the drop in core temperature during sleep: less heat produced by the body from quiet behavior and reduced muscle tone, and changes in the activity of the autonomic nervous system and of the body’s heat-control mechanisms. It adds that these patterns, and the ability to defend against heat and cold, differ between non-REM and REM sleep (Szymusiak, 2018).

NHLBI makes a related point about REM sleep: you do not have as much REM sleep in colder temperatures, because during REM sleep your body does not regulate its temperature properly (NHLBI, sleep phases and stages, last updated March 2022). We explain the stages in our guide on how sleep works.

A 2020 review says that in warm-blooded animals, sleep preparation often involves warmth-seeking, curling up and nest building, which warm the skin. It says skin warmth induces non-REM sleep and body cooling through circuitry that connects skin sensation to the preoptic area of the hypothalamus (Harding et al., 2020). The abstract describes a mechanism. It does not say how much of the evidence comes from people.

Warm Showers and Baths Before Bed

A warm shower or bath before bed is often recommended as a simple way to sleep better. A 2019 systematic review and meta-analysis searched six databases and found 5,322 candidate articles. Seventeen met its criteria, and 13 had comparable numbers that could be combined. It looked at time to fall asleep, time awake after falling asleep, total sleep time, sleep efficiency, slow-wave sleep and self-rated sleep quality (Haghayegh et al., 2019).

What its abstract reports:

Water at 40 to 42.5 °C (104 to 108.5 °F) was associated with better self-rated sleep quality and better sleep efficiency.
When it was scheduled 1 to 2 hours before bedtime, for as little as 10 minutes, it was associated with a significant shortening of the time it takes to fall asleep.
The abstract does not report findings for the other outcomes it lists (time awake after falling asleep, total sleep time, slow-wave sleep).

The authors say the results are consistent with a mechanism in which the bath increases blood flow to the palms and soles. That widens the gap between skin temperature at the extremities and at the center of the body and helps the body lose heat, so core temperature falls further. They also say the findings are limited by how little research has been reported, especially on the best timing and duration and on the exact mechanisms.

Heat in the Bedroom

A 2024 systematic review looked at ambient temperature and sleep outcomes measured in real-world settings around the world. It found that higher outdoor or indoor temperatures are generally associated with degraded sleep quality and quantity. The effect appeared across sleep measures and was stronger during the hottest months and days, in vulnerable populations and in the warmest regions. The authors add that there is limited evidence of fast adaptation to heat, and that there are opportunities to strengthen the science (Chevance et al., 2024).

A 2023 paper from the European Insomnia Network reviews how night-time temperature changes affect body temperature and sleep quality, and how this affects vulnerable groups such as older adults, children, pregnant women and people with psychiatric conditions. It suggests ways of dealing with sleep problems during heatwaves, adapted from elements of cognitive behavioural therapy for insomnia. Its authors say the literature is sparse and that many of the links it addresses should be the focus of future research (Altena et al., 2023).

On the practical side, the CDC lists keeping your bedroom quiet, relaxing and at a cool temperature among the habits that can improve sleep (CDC, About Sleep, reviewed November 2023).

What Is Uncertain

The best temperature, timing and duration for a bath. The meta-analysis authors say these need more research.
A bedroom temperature. The sources we read say “cool” and give no number, so we give none.
Cause and effect for heat. The 2024 review reports associations, and its abstract does not say how large they are.
Who should avoid a hot bath. The abstracts we read do not discuss safety. If you have a medical condition or take medication, ask a healthcare provider.
How much of the mechanism comes from human studies. The 2018 and 2020 papers are review articles that describe mechanisms, and we read their abstracts only.
Cooling products. Mattress pads, fans, pillows and similar products are outside this guide, and we make no claim about them.
Page dates. The NHLBI page shows a last-updated date of March 2022. The CDC page was reviewed in November 2023.

Questions

Does body temperature drop when you sleep?

Yes. A 2018 review says sleep in mammals is accompanied by a decrease in core body temperature, and that a rise in distal skin temperature is a prominent feature of sleep onset in humans.

Does a warm bath before bed help you sleep?

A 2019 systematic review and meta-analysis (17 studies, 13 with data that could be combined) found that a warm shower or bath at 40 to 42.5 °C was associated with better self-rated sleep quality and sleep efficiency, and, taken 1 to 2 hours before bed, with falling asleep sooner. The authors say the research is limited and more is needed.

How long and how hot should the bath be?

The meta-analysis associated 40 to 42.5 °C (104 to 108.5 °F) with better sleep quality and efficiency, and, when scheduled 1 to 2 hours before bed for as little as 10 minutes, with a shorter time to fall asleep. The authors say the best timing and duration still need research.

What temperature should the bedroom be?

The CDC says to keep it at a cool temperature. NHLBI says you have less REM sleep in colder temperatures. Neither page gives a number.

Why is it hard to sleep when it is hot?

The 2024 review found hotter temperatures generally associated with worse sleep quality and quantity. Its abstract shows the association and does not explain why.

Sources Cited in This Guide

Szymusiak R. “Body temperature and sleep.” Handb Clin Neurol. 2018. Read September 20, 2026 (abstract). PMID 30454599
Harding EC, et al. “Sleep and thermoregulation.” Curr Opin Physiol. 2020. Read September 20, 2026 (abstract). PMID 32617439
Haghayegh S, et al. “Before-bedtime passive body heating by warm shower or bath to improve sleep: A systematic review and meta-analysis.” Sleep Med Rev. 2019. Read September 20, 2026 (abstract). PMID 31102877
Chevance G, et al. “A systematic review of ambient heat and sleep in a warming climate.” Sleep Med Rev. 2024. Read September 20, 2026 (abstract). PMID 38598988
Altena E, et al. “How to deal with sleep problems during heatwaves: practical recommendations from the European Insomnia Network.” J Sleep Res. 2023. Read September 20, 2026 (abstract). PMID 36073025
National Heart, Lung, and Blood Institute, NIH. “How Sleep Works: Sleep Phases and Stages.” Last updated March 24, 2022. Read September 20, 2026. NHLBI
Centers for Disease Control and Prevention. “About Sleep.” Published May 15, 2024; reviewed November 20, 2023. Read September 20, 2026. CDC

This guide is for information and is not medical advice. Talk to a healthcare provider about medication, pregnancy, medical conditions and persistent sleep problems.