The sleep-friendly bedroom: temperature, light and noise

Articles on the "ideal sleep temperature" usually quote one number. The research does not support one. A 2012 review of thermal-environment studies found that when people slept with normal bedding and clothing, sleep did not differ significantly across room temperatures from 13 to 23°C (about 55 to 73°F), and in another study from 3 to 17°C.^[1] Bedding and clothing do most of the work. What matters is the bed climate: the pocket of air between your skin and the covers.^[1]

The same review is clear about what does hurt. With bedding and clothing on, heat increases wakefulness and reduces slow-wave (deep) sleep and REM sleep, and humid heat adds to the load.^[1] The 29°C (84°F) "thermoneutral" figure that sometimes gets quoted comes from people sleeping nearly unclothed, not from a normal bedroom.^[1]

Cold works differently. With covers, cold did not change sleep stages, but it did change heart activity during sleep without people noticing it, which is why the review's authors say a bedroom in winter should stay above 10°C (50°F).^[1]

In practice, the goal is not to hit a number but to stop the room and the bed from getting hot. A fan or air conditioning in warm weather, lighter and more breathable bedding, and a mattress that does not trap heat all work on the same problem. If the room is hot and humid, bringing the humidity down matters as well as the temperature.

In a study of 116 healthy adults aged 18 to 30, spending the eight hours before bed in ordinary room light (under 200 lux) instead of dim light (under 3 lux) delayed the start of melatonin release in 99% of people and shortened the body's melatonin night by about 90 minutes.^[2] Room light during the usual hours of sleep suppressed melatonin by more than half in 85% of trials.^[2]

Light during sleep itself matters too. In a 2022 laboratory study, healthy adults who slept one night in moderate (100 lux) light had a higher heart rate during the night and more insulin resistance the next morning than when they slept in a dim room.^[3]

In practice: dim the lights in the evening, and make the room itself dark while you sleep. Blackout curtains deal with streetlight and early sunrise; a sleep mask does the same job with nothing to install, and travels. If a fully dark room makes mornings hard, a sunrise alarm clock brightens gradually at your wake time.

Environmental noise disturbs sleep and causes daytime sleepiness, and long-term exposure is linked with high blood pressure and heart disease.^[4]

The most popular fix, a white noise machine, has weaker support than its sales suggest. A 2021 systematic review of 38 papers rated the quality of evidence that continuous noise improves sleep as very low, and warned that it may also harm sleep and hearing.^[5]

Earplugs have somewhat better, though still limited, evidence. In a laboratory study, healthy people exposed to recorded intensive-care noise and light got more REM sleep, fewer arousals and higher melatonin when they wore earplugs and eye masks.^[6] A Cochrane review of intensive-care patients found low-quality evidence that earplugs or eye masks increase total sleep time, though most of the studies that measured sleep directly found no benefit.^[7]

In practice: reduce noise at the source where you can, then block what is left with earplugs. If you use a sound machine to cover intermittent noise, keep the volume low and treat it as a comfort rather than a treatment.

Some of the most shared bedroom advice has no sleep research behind it. We searched PubMed for studies testing bedroom wall colour against sleep and found none. A calming colour may make a room more pleasant to be in, but we found no study showing it changes how you sleep.

Aromatherapy is a different case: it has a small trial literature of its own, which our aromatherapy guide goes through. It is not covered here because it works on the person, not on the room's temperature, light or noise.

If you have fixed heat, light and noise and still sleep badly, the cause is probably not the room. Caffeine timing is the next thing to check, and it has its own guide on this site.