What makes a bedroom good for sleep?

Some nights the trouble seems to be the room itself. You're awake in the small hours and too warm, with the covers half off, and a light you hardly noticed by day catches the edge of your eye. It's easy to lie there sure that something about the place is keeping you up.

Sleep is something your body already knows how to do, and the room's whole job is to stop interrupting it. As night comes on, your core temperature starts to fall, and sleep comes most easily while it's falling¹1 Okamoto-Mizuno & Mizuno, 2012. To help it along, the body opens up the blood flow to the skin of your hands and feet and lets heat go there¹, out into the air under the covers. If you're lying awake and too warm right now, that's the part you can help with before reading on.

The warmth leaving through your hands and feet is the body bringing its core temperature down, so falling asleep is partly a matter of cooling. When researchers warmed people's feet to open those vessels further, they fell asleep faster¹1 Okamoto-Mizuno & Mizuno, 2012. If your feet are cold in bed, that cooling has a harder time getting going, and socks or a hot-water bottle may help on the same idea: warming the feet until their vessels open and the heat can leave.

What your skin feels through the night is mostly the small pocket of air between you and the covers. In people sleeping normally, that pocket stays warm and fairly steady¹ more or less whatever the room is doing, as the figure below shows. It's the covers that set what your skin feels, so the duvet, the sheets and what you wear count for as much as the thermostat.

In lab studies where people slept under ordinary covers, too warm a night disturbed sleep more than a cool one, and the trouble came mostly in the early hours. Those are the hours of a hot night when you lie restless, awake more than you'd like, with less¹ deep sleepdeep sleep The slowest, most settled stage of sleep, when it’s hardest to wake someone. Most of it comes in the first part of the night. and REM sleepREM sleep Rapid eye movement sleep, often called dreaming sleep: the stage when most vivid dreaming happens. The eyes move quickly beneath the lids while most of the body’s muscles stay relaxed and still. than a cooler night would bring. In one of the studies the sleepers still hadn't adapted after five days¹ of heat. A cool room is the easier of the two to live with, since you can pull up a layer when you need one.

In a heatwave without air conditioning, being told to keep the room cool can sound almost like a taunt. The walls give off the day's warmth long after dark and the sheet clings to your back. Humid heat is the hardest kind. When sweat can't evaporate, the body can't shed its heat¹1 Okamoto-Mizuno & Mizuno, 2012, and people lie awake longer.

One survey of US adults gathered 765,000 responses and matched them to local nighttime temperatures. Each 1.8°F (1°C) of unusually warm night meant about three extra nights of poor sleep a month for every hundred people⁴4 Obradovich et al., 2017. That was sleep as people reported it, and the effect was strongest in summer, in people over 65 and in people on lower incomes⁴. The researchers wondered whether air conditioning, and who can afford it, explains the income gap. That was their guess, and they didn't measure it.

So what about a fan? Reviewers went looking for trials of fans in heatwaves and found none. None of the research they read looked at sleep⁵5 Gupta et al., 2012, either. The case for a fan rests on what it does at your skin: it moves air across it and helps the sweat dry, so the heat has somewhere to go. A single sheet can stand in for the duvet. If you have cooling of any kind but can only run it for part of the night, the researchers suggest the first few hours of sleep¹ are when it matters most. If you wake later damp with sweat, drying off and changing into dry clothes¹ can keep you from waking chilled before dawn, so it helps to leave something dry within reach.

Older people's sleep seems to be more sensitive to heat. In small studies of older men, even mild warmth added time awake¹, and in one it also doubled how much they sweated overnight¹, so a glass of water by the bed is worth having on hot nights.

None of this applies to babies, whose rooms and bedding follow their own safety guidance, which you'll find in how to keep a newborn safe.

The light you notice at night is often small: a streetlight in the gap between the curtains, or the red glow of a standby light across the room. Most of the ways to shut it out cost very little. An eye mask does the job, and so does something pinned over the gap or a scrap of tape over the light. Blackout blinds do the same for the whole window.

What you're after is a room dark enough that light doesn't wake you or keep you stirring. In a study of older adults in their sixties to eighties, those whose wrist sensors picked up any light in the darkest hours of the night spent more time awake after first falling asleep²2 Kim et al., 2023. It's a link, and it doesn't show that the light was the cause.

If you're curious about light's wider effects on the body and its clock, how light affects sleep goes further into it.

All night the sleeping brain keeps half an ear open. What wakes us is less the overall level of sound than the number of separate noises³3 Basner & McGuire, 2018: a door, a motorbike, a voice on the stairs. In sleep-lab recordings, each ten-decibel rise in the peak sound of a passing plane, car or train raised the odds of waking by about a third³, whichever it was.

We do get used to a street, but how far does that go? Years on, the sleeping brain still reacts to the noise, and the heart and nervous system get used to it even less³ than the brain does. So the person who says they no longer hear the trucks may be right about waking and still be stirred by them.

If it's the street or the house that wakes you, earplugs are the most direct answer. In one small trial, researchers had healthy volunteers spend a night in a sleep lab with recorded intensive-care noise and light playing. Those given earplugs and an eye mask woke less often and fell asleep faster⁶6 Huang et al., 2015. When others looked at real patients in intensive care, most of the studies that measured sleep directly found no benefit⁷7 Hu et al., 2015. None of the research read here tested them in an ordinary bedroom at home, but earplugs cost little and the reasoning behind them is plain, so they're worth a few nights' try anyway.

White noise rests on the idea of masking those changes under a steady sound. Some people find a fan's hum or a rain recording helps them drop off. The studies point both ways: in some, steady noise helped sleep, and in others it disturbed it⁸8 Riedy et al., 2021. There's also an open question about its effects on hearing. If a sound helps you, there's no reason to give it up, though it's worth keeping the volume modest.

A fair question to ask of any of them is what it stops interrupting, and the cheap things answer it most clearly. Earplugs stop the changing sounds that rouse you, a mask or blackout blinds stop the light, and a fan helps heat leave your skin. Each costs little and has plain reasoning behind it.

If a cooling mattress is in your basket, it has a real answer too, and the size of it is useful to know. When people slept on a heat-absorbing mattress in a sleep lab, they gained about seven and a half minutes of deep sleep over a seven-and-a-half-hour night⁹9 Herberger et al., 2024. People responded very differently, so the average may tell you little about your own nights. One of the researchers works for a mattress maker, too.

For mattresses in general, the answer comes down to comfort. Reviews favor medium-firm¹⁰¹¹10 Caggiari et al., 202111 Radwan et al., 2015, but the studies disagree, and each judges firmness its own way. The best guide is what feels comfortable to you over a few weeks. A scent or a pillow spray is harder to place. Some studies found people slept better with scents, but the gains showed mostly in the weaker studies and in aroma massage¹²12 Her & Cho, 2021, which tells you little about a spray on the pillow by itself.

Then you're two bodies with two sets of needs under one blanket, and often one of you runs hot while the other's cold. The studies found two things that are both true to life. In the few studies that measured it, people moved more and slept somewhat differently¹³13 Troxel et al., 2007 with a partner in the bed. Yet most said they slept better together, and women in one study said a partner made them feel more secure¹³.

A small first step is two duvets on the one bed, each of a weight that suits the person under it. The one who runs hot can sleep under something thin while the other stays wrapped up. Sometimes what one of you brings to the bed is snoring. For the one lying awake beside it, that's a sound that keeps changing, so it seems fair to expect it to disturb sleep the way separate noises tend to³3 Basner & McGuire, 2018. Earplugs or a steady sound, as in the part on noise, are an untested but cheap thing to try. Where a couple's sleep problems are getting in each other's way, researchers suggest that splitting the bed or using a second room may help them cope¹³, and that sleeping apart needn't strain the relationship. Nobody has put that to a direct test, so it stays a choice for the two of you, made around how each of you sleeps.

If you sleep after a night shift, you're sleeping against daylight, deliveries and the school run. On top of the body clockbody clock The timekeeper in your brain that runs on a cycle of about a day, setting when you feel sleepy and when you feel alert. Daylight, especially in the morning, keeps it in step with the clock on the wall., noise and the obligations of daytime life interrupt that sleep¹⁴14 Sack et al., 2007. In a small study of thirty permanent night workers, the body clocks of those who slept in a darker bedroom by day adjusted further to nights¹⁴. It's an association, but it makes darkening the room a sensible, low-cost place to start. You could try foil on the glass, a heavy curtain pinned over the existing one, an eye mask and earplugs against the street, and none of them means changing the window. None of these has been studied in day sleepers themselves. Timing your sleep and light around shifts has its own page, how to sleep well on night shifts.

If you rent on a busy road, share a room or live in a small flat that stays hot from the day, the things that travel with you do the most good: earplugs and an eye mask, a lighter layer on the bed, a window opened for the first hours of sleep, and dry clothes within reach for a sweaty waking. An open window lets the street in along with the cool, and earplugs are how you can have both. A fan's hum is a steady sound too, the kind some people find helps them sleep, as in the part on noise.

If the poor nights follow you from room to room, the room probably isn't the cause, and a better one is unlikely to set it right. For insomniainsomnia Trouble falling asleep, staying asleep or waking too early, that keeps happening and affects how you feel or get on during the day. that has gone on for months, the sleep doctors' guideline advises against counting on a better room and good habits, what's often called sleep hygienesleep hygiene Everyday habits often suggested for better sleep, such as keeping caffeine to the first part of the day, sticking to regular hours and sleeping in a dark room away from noise., as the treatment on their own¹⁵15 Edinger et al., 2021. What it firmly recommends is CBT for insomniaCBT for insomnia Cognitive behavioral therapy for insomnia: a short course of practical, talking-based techniques that help retrain sleep. It’s the first treatment doctors recommend for long-term insomnia.. One part of that, stimulus controlstimulus control A part of insomnia treatment that helps the bed feel linked with sleep again: going to bed when sleepy, and getting up for a while when sleep won’t come., keeps the bed for sleep alone, so that over time lying down comes to mean sleep again. Do I have insomnia? and what CBT for insomnia would ask of you take that further.

A room can't fix loud snoring with pauses in breathing or gasping in the night, or sleepiness in the day despite enough time in bed. These are the signs a doctor looks at¹⁶16 Kapur et al., 2017 for sleep apneasleep apnea A condition in which the throat repeatedly narrows or closes during sleep, briefly stopping or reducing breathing. Loud snoring, gasping and daytime sleepiness are common signs.. If you or someone beside you notices them, they're worth taking to a doctor. If you're the one lying awake beside the snoring, whether to worry about a partner's snoring looks at it from your side of the bed.

For everyone else, the list is short and mostly cheap: a layer you can throw off, a window or a fan, something to make the room dark, and earplugs if the street or the house keeps waking you. It helps to make the changes before bed and then let the room be for the night. You may remember sleeping best in a borrowed bed, a hotel room on holiday or a friend's sofa after a long day. In each of them you felt safe, and nothing needed seeing to.