Why is it so hard to sleep when it's hot?
Because falling asleep starts with your body shedding heat: your core temperature drops through the evening. A warm, humid bedroom fights that, so you fall asleep later and wake up earlier.
Warm skin that can't shed its heat.
Your core can't cool enough to drift off.
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Sleep starts with cooling down
About two hours before your usual bedtime your core temperature starts to fall. Blood vessels in your hands and feet widen to dump heat, which is why your feet can feel warm as you get drowsy. The drop continues through the night and bottoms out in the early morning.
That's why sleep experts suggest a cool bedroom, about 65°F (18°C). Much warmer and your body struggles to get rid of the heat it needs to lose.
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What warm nights do
A study of about 7 million nights of sleep, recorded by wristbands on more than 47,000 people in 68 countries, found that on nights above 30°C (86°F) people slept about 14 minutes less on average and were more likely to get under seven hours. Mostly, the heat delayed falling asleep. Older adults were hit harder.
Humidity makes it worse. If sweat can't evaporate it can't cool you, so a 78°F night with a high dew point feels far stuffier than a dry one.
Why some nights stay warm
Clouds and humid air hold in the day's heat, a breeze keeps the air stirred so it can't cool at the ground, and cities soak up heat in pavement and brick and release it all night. Air Story's On you panel shows tonight's expected low, and the trail shows whether your warm night arrived from somewhere hot.
Questions people ask
- What's the best temperature for sleeping?
- Sleep experts commonly suggest about 65°F (18°C), in a range of roughly 60 to 68°F.
- Does humidity affect sleep?
- Yes. Humid air slows the evaporation of sweat, so your body cools less well and the room feels warmer than the thermometer says.
- How can I sleep better on a hot night?
- Close blinds during the day, cool the room before bed, keep a fan moving air over your skin and use light bedding. Air that moves helps sweat evaporate.