The perfect temperature for sleep—and how to get it
The Goldilocks equation for the best night's rest—it's easier to solve than you think.
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We’ve all had those nights in the summer, or even during unseasonably warm winter nights: sweaty and sleepless. But what’s actually going on when your room is hot and you can’t sleep? And why doesn’t anyone talk about the opposite extreme—a room that’s too cold?
While the effects of bedroom temperature on sleep are often overlooked, they can be the difference between a great and a terrible night’s rest. At either extreme, too hot or too cold, your body is trying to actively regulate its temperature to keep it optimal for normal body functions, including (and especially) sleep. Researchers found that living in cold climates is metabolically expensive, meaning these conditions require significant energy output. And if your body is doing all that overnight … Well, you’re not exactly getting the best rest. So when it comes to temperature and sleep, you really have to hit the sweet spot.
Does your body temperature drop when you sleep?
As it turns out, not only does body temperature decrease while you doze, it goes through changes all day long. In fact, if you regularly took your temperature throughout the week and graphed it, you would get a sine wave (think the shape that cartoon drawings of Nessie take—multiple S’s connected horizontally), says W. Christopher Winter, MD, sleep expert, and author of "The Sleep Solution." In other words, your temperature routinely peaks in the mid to late afternoon then cools down, dropping to its coolest point around 5 a.m., and then starts climbing back up, and repeats the cycle, he says. This pattern also corresponds with light levels, and our circadian rhythm, the 24-hour cycle that governs most of our days.
Not only that, an evening decrease in body temperature, in keeping with your daily temperature waves and shifts, precipitates drowsiness and helps your body register that it’s getting close to bedtime. Changing your environment to match your core temperature’s shifts can help you sleep—and wake up—feeling better.
What is the best temperature for sleeping?
Few people will ever say they slept well when it’s hot, Winter says. That's because for the vast majority of people, cooler is better. Sleeping in hotter temperatures has been found to trigger changes in sleep patterns and quality. Researchers found that hotter temperatures can decrease the amount of “slow wave” sleep and REM sleep (a.k.a. the part of your sleep cycle when you dream) that people get during a given night. Slow-wave sleep occurs during the third stage of sleep (after REM sleep, and stages one and two, which are marked by successively slower brain activity and heart rate), and is colloquially known as “deep sleep.” Deep sleep is the most restorative and restful part of the night. Good deep sleep helps you feel awake and refreshed the next day, and research suggests it’s important for learning and memory.
Of course, on the opposite extreme, bedrooms can also be too cold for quality rest for some people. As with everything related to sleep, it boils down to personal preference and what leaves you feeling refreshed in the morning. Nighttime temperatures should generally be cooler than what you prefer during the day—most experts suggest in the mid-60s. Even if that sounds cold to you, you should try it for at least a week, Winter says. Sleep is influenced by many factors, and if you give it just one night and don’t sleep well due to other variables, you might attribute your restlessness to the thermostat. So ride it out. If you normally keep the temperature at 75°F all day and night, drop it to 68°F at night for a week and see what happens to your sleep, he says.
Can being cold make me tired?
By now you might be thinking: How can I support my body in its quest to find the perfect temperature for optimal sleep? Taking a warm shower or bath at night might sound counterintuitive—you want to cool off, not heat up, after all. But for some, it can work. The warm water will raise your core temperature, but the key is what happens after you get out of the water. Most people’s core temperature will drop rapidly because the ambient air is cooler than the hot water you bathed in, and that’s the important piece. If you’ve ever gotten out of a hot tub in the evening and felt drained, you’ve experienced the sensation. This decrease could help you feel tired, and may put you on the right track to sleep.
Exercise can also raise your body temperature, but exercising right before you plan to hit the hay isn’t generally recommended. That isn’t to say working out in the evening is bad, but when you inch closer and closer to bedtime, physical activity can be stimulating, which can make it harder to fall asleep. Ideally, you’ll wrap up any vigorous exercise at least one hour before you plan to go to bed.
What can I do to manage temperature overnight?
Some nights you might go to bed freezing and wake up sweating in the middle of the night (or vice versa), and changes in body temperature throughout the night can be uncomfortable and disruptive to your sleep. Fortunately there are a few ways to manage them, or at least decrease the time you spend awake after realizing you’re too hot or cold.
For starters, Winter recommends avoiding wearing heavy pajama pants to bed and sleeping in light clothing, or even nothing at all. You might feel cool when you go to sleep, but if you wake up in the night because you’ve gotten too hot, it’s a hassle and a disruption to get up—maybe turning on the light—and free yourself from the warm fleece pants that seemed like a good idea just a couple hours before.
The best way to deal with fluctuation in room temperature that may occur overnight and your own thermoregulation is to use layers—and not layered clothing, but rather, layered bedding. That way, if you wake up too hot, you can just throw off one blanket and doze right back to sleep, he says. And if you wake up too cold, there's an extra blanket on standby.
How can I make the temperature in my bedroom optimal for sleep?
Beyond clothing and bedding, there are other options for controlling your environment. Setting the temperature on the thermostat to the mid-60s for the night is a good idea, and things get even better if you have a smart thermostat. Winter thinks many people don’t use these devices to their true and full potential in the context of improving sleep. Many smart thermostats including our favorite, the Emerson Sensi Touch Wifi Thermostat, have schedule functions, says Reviewed’s senior scientist, Julia MacDougall, who wrote our review. “Oh yeah," she says, "the scheduling on these things works.”
The schedule settings can be fine-tuned to follow certain patterns, including dropping the temperature in stages: once in the early evening and then again, say, an hour before you’ll be going to bed. Of course, those adjustments can be done manually with any other thermostat, it’s just a bit of a hassle. But where a smart thermostat wins is its ability to schedule a warm-up in the morning before your alarm goes off. Raising the temperature about an hour before you would like to spring out of bed can help make the morning a little easier. “It’s a really great tool for people who struggle to wake up in the morning,” Winter says.
If you don’t have control of your own heat (and it’s cooler outside), consider opening your windows before you go to bed to cool your room down, and lowering it to a crack for the the night to keep cooler air circulating.
What products can I use to improve my sleep?
The problem with thermostats is that they control the entire space, not just a fraction of the room. So maybe you’re a cold sleeper, but your partner bakes overnight. Who wins the thermostat battle? Not to forget about the folks who don’t have thermostats or who live in warm climates and don’t have AC. Fortunately, there are products and techniques to control just your climate bubble as you snooze.
We reviewed the Chilipad Sleep System, which is a mattress pad specially designed to cool or warm the bed beneath you. The Chilipad works by circulating temperature-adjusted water through the pad. Our reviewer said it was responsive, albeit not perfect. It comes in typical bed sizes and in a single size, so you can control just half of the bed.
If you’re looking for a simpler (and less expensive) solution, focus on keeping your head cool. It’s true that just targeting your head can drastically improve your sleep and help you cool down, Winter says. Plus, there are numerous possible approaches. Winter has patients who freeze their pillowcases and put them on just before they go to bed. One of our editors, who lives in the Caribbean, takes a lukewarm shower before bed and finds that having wet hair as she dozes works like personal evaporative air cooling. Pillows with cooling properties are another way to keep your head cool. I had luck with the Tempur-Cloud Breeze Dual Cooling Pillow. Even through a protective pillow cover and pillow case, I could feel it chilling my head. The nice thing about cooling pillows is, unlike an icy-cold pillowcase or damp hair, it won’t eventually lose its chill. The pillow has “Tempur-breeze” gel material on both sides. The company doesn’t provide an explanation of what it actually is, or how it’s made—but if it works, it works.
Some mattresses and bedding also claim to have cooling properties. I’m not sure the efficacy of cooling mattresses, and in our mattress testing, we found that some are warmer than others. Bedding, however, can be as simple as choosing the right fabric for sheets. Cotton is known for its breathability, and has a reputation for feeling cool. It’s also absorbent, so you’re unlikely to wake up damp with sweat, which contributes to their cool sensation. As it turns out, science backs up cotton’s anecdotal cooling benefits—the chemical structure of cotton, and the fiber’s “large surface area” make it feel cool throughout the night. The tester of our best bed sheet sets says she woke up feeling cool even on hot days after sleeping on Brooklinen’s Luxe Core Sheet Set. For cold sleepers, flannel sheets are great because their napped surface and fuzzy texture make them feel warmer, plus if you purchase a set made from cotton, you’ll find the fabric retains key characteristics, like breathability.
Before buying a pricier product that claims to keep you cool overnight, just be sure to look at the company’s return policy. Companies that give you the option to products on for size and be sure they work for you, without stipulations are always a good idea. Chilipad offers returns within 90 days of purchase. Tempur-Pedic also permits returns on used mattresses within 90 days. Other products, including their pillows, can’t be returned unless there’s a manufacturer defect or it’s damaged at delivery.