Why You Wake Up Hot at 2 A.M., and What to Change About Your Bed

You went to bed comfortable. Now it's 2 a.m., one leg is outside the covers, and you're flipping the pillow to find the cool side.

Most people blame the thermostat. Often, the bigger problem is the small pocket of air trapped between you and your bedding.

The good news is that this pocket is easy to change, and you don't need a new mattress to do it.

Your body is trying to cool down all night

Falling asleep is partly a cooling process. According to the Sleep Foundation, your body temperature starts dropping about two hours before you go to sleep, and it keeps falling through the night until the early morning.

Your bed can help with that or get in the way. When heat has nowhere to go, you feel it, even if you never fully wake up.

Researchers have looked at this directly. A review of studies on sleep and thermal environment found that when people sleep with bedding and clothing, heat exposure increases wakefulness and reduces both slow wave and REM sleep. Humid heat made wakefulness worse.

So a hot, damp bed can cost you more than comfort. It can also cost you some of your deepest sleep.

The climate you actually sleep in

That same review describes something called the bed climate, which is the temperature and humidity in the space between you and your covers.

When people sleep normally, it reports, that space generally stays around 32°C to 34°C, or about 90°F to 93°F, with 40% to 60% relative humidity.

Your thermostat controls the room. Your bedding controls this much smaller climate, and it sits right against your skin. That's why two people can sleep in the same 68-degree room and have completely different nights.

Start with the room

Fix the easy part first. The Sleep Foundation says the ideal temperature for sleep is between 65°F and 68°F, so check where your thermostat actually sits at bedtime.

A few other simple moves help:

Set the temperature to drop about an hour before bed, not when you get in.
Run a fan to keep air moving across the bed.
Close the blinds during the day so the bedroom doesn't store up heat.
Take a warm shower before bed, not a hot one right as you lie down.

Then fix what's touching your skin

Sheets are the layer most people overlook, and they're the cheapest part of the bed to change. Three things matter most when you're shopping.

Fabric. This is the big one. Cotton breathes and lets heat escape, while polyester and microfiber tend to hold heat against your skin. If your current set feels slick and you wake up clammy, start here.

Weave. Percale feels crisp and airy, like a hotel sheet. Sateen feels smoother and a little heavier. Both can work in natural fibers, so choose by the feel you like.

Freshness. Sweat and body oils build up in fabric, and sheets that have gone a little stale never feel as good at bedtime. Some sets now come with a silver finish that the makers say helps limit odor-causing bacteria on the fabric, which can stretch the time between washes.

Be wary of any set that promises to be ice cold all night. Fabric can't refrigerate you. What good cooling sheets can do is let heat and moisture move away from your body, so that small climate under the covers doesn't turn into a sauna.

Because feel is so personal, look for a brand with a long trial period. A few nights in a store won't tell you much, but a few weeks in your own bed will.

Don't forget the rest of the bed

Once your sheets are sorted, look at what's on top of them and underneath them.

Comforter. A heavy down or synthetic comforter can undo the benefit of a breathable sheet. In warm months, try a lighter one or just a blanket.
Mattress protector. Some waterproof protectors trap heat. If your bed got hotter after you added one, that could be why.
Pajamas. Light, breathable fabric beats heavy synthetics. Clothing is part of the same bed climate.
Partners. If one of you runs hot, use two separate lightweight blankets instead of sharing one thick comforter.

When it might not be your bed

If you're regularly waking up drenched in sweat, even in a cool room with light bedding, mention it to your doctor. Night sweats can have medical causes, and no set of sheets will fix those.

The bottom line

Sleeping cool comes down to two climates: the room and the small space under your covers.

Set the thermostat between 65°F and 68°F, keep the air moving, and choose breathable bedding that lets heat escape. It's a small change, and it could be the difference between a full night's sleep and another 2 a.m. pillow flip.