Experiment guides → Bedroom & environment → Cooler bedroom
Do you sleep better in a cold room?
Quick answer: cooler than most bedrooms, yes — but the evidence says "not hot" more than it says "cold". Your core temperature has to drop about 1°C for sleep to start, and a warm room fights that; heat exposure reliably increases wakefulness and cuts deep sleep. The best real-world data — 11,000 nights from older adults' own bedrooms — found sleep was most efficient between 20 and 25°C, dropping 5–10% as the room rose toward 30°C. Below about 18°C the picture depends on your bedding, and cold feet actively delay sleep onset. The useful experiment isn't "as cold as possible"; it's picking one temperature in the cool range and holding it for 14 nights.
"I will keep my bedroom at 19°C for 14 nights."
What the research says
Heat is the clear enemy; cold is conditional. Okamoto-Mizuno and Mizuno's review of thermal-environment studies concludes that heat exposure increases wakefulness and reduces both slow-wave and REM sleep, and that humid heat is worse still. Cold exposure, by contrast, mostly affected cardiac autonomic activity rather than sleep stages — provided bedding and clothing were adequate. The authors call the thermal environment one of the most important factors in sleep (Okamoto-Mizuno & Mizuno, 2012).
Why: sleep starts when the core cools. Harding, Franks and Wisden lay out the physiology: sleep onset is coupled to a fall in core temperature, achieved by shunting heat out through the hands and feet. A warm room blocks that heat loss; warm skin (a bath, socks) paradoxically speeds it. The sweet spot is a cool room with warm extremities — which is why "cold room" and "cold feet" are opposite advice (Harding et al., 2019).
The real-bedroom numbers: 20–25°C. Baniassadi and colleagues tracked 50 older adults at home for a year with bedroom temperature sensors and wearable sleep monitors — about 11,000 nights. Sleep efficiency and restfulness were highest between 20 and 25°C and fell by 5–10% as the temperature rose from 25 to 30°C. The optimum varied noticeably from person to person, which is the argument for testing your own number (Baniassadi et al., 2023).
What this evidence doesn't say
The home-monitoring study was in older adults, whose thermoregulation differs, and it observed rather than set temperatures. Lab studies use conditions (fixed bedding, controlled humidity) that don't match a real bedroom, and the popular "16–18°C" advice isn't a number any of these studies produced. Your bedding, partner, pyjamas and humidity move the optimum, so the range is a starting point, not a prescription.
Run it as an experiment
- Measure before you change anything. Put a cheap thermometer by the bed and note the temperature at lights-out for five baseline nights, alongside sleep quality, restedness and time-to-sleep. Most people are surprised by their number.
- Pick one target in the cool range. If your baseline is 22°C or above, try 19°C. If you're already at 19, the experiment may be bedding (a lighter duvet) rather than the thermostat. Change one thing.
- Make the pact. "I will keep my bedroom at 19°C for 14 nights." Window, thermostat or fan — whichever gets you there consistently. Keep the duvet the same throughout.
- Keep your feet warm. If you wake with cold feet, wear socks rather than raising the room. Cold extremities delay sleep onset even in a well-set room — it's the one variable worth fixing mid-experiment, with a note.
- Compare, and adjust by two degrees if needed. Better restedness and fewer wakings? Keep it. Colder felt worse (cold feet, waking chilled)? Retest at 21°C. Your optimum is a number, and two 14-night blocks will find it.
What to expect
If your room was warm, the difference is often noticeable within a few nights: fewer sweaty wakings in the second half of the night, and an easier drop-off. If your room was already cool, expect little from going colder — and don't mistake shivering for progress. Summer heat is where this experiment pays off most; a fan, a lighter duvet and an open window are all fair ways to hit the target.
Who should skip this
Infants, older adults with poor circulation, and anyone with Raynaud's or a condition affecting temperature regulation should not chase a cold room; keep bedrooms comfortable and talk to a doctor. If you share a bed with someone who runs cold, a lighter duvet on your side beats a thermostat war.
Frequently asked questions
What is the best bedroom temperature for sleep?
The best real-world data put peak sleep efficiency between 20 and 25°C in older adults, with a clear decline above 25. The widely quoted 16–18°C isn't a figure from these studies. A sensible starting target for most adults is 18–20°C with adequate bedding — then test.
Does sleeping in a cold room cause nightmares?
There's no evidence for it. Disturbed sleep in a cold room usually traces to cold feet and hands, which fragment sleep and delay onset; warm socks fix that without warming the room.
Is a cold room good for deep sleep?
Heat is what robs deep sleep — studies consistently show less slow-wave sleep in warm conditions. A cool room removes that obstacle. Going colder than cool doesn't add deep sleep; it just risks the cold-extremity problem.
Related experiments
Sources
- Okamoto-Mizuno K, Mizuno K. Effects of thermal environment on sleep and circadian rhythm. J Physiol Anthropol. 2012;31:14. PubMed 22738673
- Harding EC, Franks NP, Wisden W. The temperature dependence of sleep. Front Neurosci. 2019;13:336. PubMed 31105512
- Baniassadi A, Manor B, Yu W, Travison T, Lipsitz L. Nighttime ambient temperature and sleep in community-dwelling older adults. Sci Total Environ. 2023;899:165623. PubMed 37474050
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Downloadon the App StoreThis page is general information about published research, not medical advice. If you have a sleep disorder, are pregnant, or take medication, talk to your doctor before changing your routine.