Why it’s so difficult to sleep in the heat – and what can you do about it
Is there anything more bothersome than trying to sleep in the heat? You toss and turn, flipping the pillow over and over to try to find the cool side, coated in a sticky sheen of sweat. Nothing you do seems to help you sleep.
So why is it so difficult to sleep in the heat and what can you do about it?
Temperature is an incredibly important facet of falling asleep, explained Dr Guy Meadows, the co-founder and clinical director of the Sleep School app.
He said: “Our core body temperature plays an important role in the regulation of sleep. At the start of the night, a 1C drop in temperature is needed to help you fall asleep.
“It’s this decrease, coupled with the arrival of darkness, that informs the internal body clock that the night has begun. This triggers the release of the sleeping hormone melatonin, helping you fall asleep.
“We sleep better in a cool room, compared to a warm room, with the ideal temperature reported to be 16C-17C,” said Dr Meadows, although that does take into consideration that most of us wear something to bed and use various amounts of bedding.
What temperature is too hot to sleep in?
It goes without saying that different people will have different tolerances for the temperatures they can sleep in. Someone who lives in Arizona will be more used to the heat than another person from Siberia. Similarly, young children and older people tend to require a slightly warmer sleeping environment.
However, the mercury needn’t be soaring for it to prove difficult to sleep. A 2020 study from Waseda University in Japan found that it becomes more difficult to sleep when the temperature climbs over 24C.
What are the effects of sleeping in a hot room?
Ultimately, trying to rest in a hot room will make it harder to fall asleep and you’ll sleep less efficiently once you do.
Another study, published in 2012 by scientists at Tohoku Fukushi University, also in Japan, found that increasing the temperature in a bedroom by 6C meant sleepers spent 6.8 per cent more time awake and reduced their sleep efficiency by seven per cent.
One 2015 study, again from Japan, found that the slow-wave (deep) sleep that our body uses to heal and restore itself is reduced when sleeping in the heat. This means that the following day, fatigue is far more likely.
How to sleep better in the heat
“Sleeping well in the heat involves mastering the art of controlling that which you can change, and accepting that which you can’t,” advised Dr Meadows.
“There are many practical actions that you can take to keep cool during a heatwave that will promote better sleep. However, sometimes adopting an accepting attitude can be the best approach.”
Keep your head cool by keeping a cool head
Dr Meadows added: “Getting frustrated and restless because you’re too warm only makes your body generate more heat, keeping you awake for longer. Keep cool by lying still and accepting the heat.
“Try focusing your attention on the discomfort and describe what you feel objectively and without judgment, such as ‘I feel heat and sweat on my face, neck and back’. Learning to change your relationship with the heat helps defuse its power and lead to better sleep.”
Prepare for cooler sleeping during the daytime
It might sound counterintuitive, but keeping your curtains closed can stop your bedroom getting warm in the first place, making it easier to fall asleep at night. Another thing to do is to avoid a late dinner.
“Eating food close to bedtime elevates your body temperature, making it harder to sleep,” said Dr Meadows. “For the best night’s sleep, leave at least two hours between eating and sleeping – and limit alcohol consumption.”
Wear cotton pyjamas or sleep naked
“If you’re wearing natural fibres like cotton, then you’ll feel cooler in the night than if you were naked, because the cotton will wick away sweat from your skin,” said Dr Alanna Hare, an NHS and private sleep consultant at the Royal Brompton Hospital.
“However, anything man-made or synthetic will keep heat next to your skin. And the same goes for bedding. So if I had the choice between cotton and nakedness, I’d choose cotton. But if you’re choosing between man-made fibres and nakedness, go naked.”
Create a breeze
“Sleep with the window open or keep a fan on during the night to add an extra breeze in your bedroom,” Dr Meadows advised.
If you want to keep things extra cool, place a frozen bottle of water between yourself and the fan to cool the air as it comes towards you. (Modern air coolers can chill the room by a few degrees using this principle.)
Make a ‘cold water bottle’
“Simply fill a hot water bottle with cold water and keep it in the fridge or freezer for a few hours before bed – if you’re an extra hot sleeper, you can leave it in a little longer,” suggested Chris Tattersall, a sleep expert at bedding manufacturer Woolroom.
“Then snuggle up with your ice pack under the covers or leave it to cool down the bed before jumping in – it’s one of the best ways to keep cool at night.”
Ditch the memory foam
“The synthetic materials used in a memory foam mattress mean that it’s not breathable and doesn’t absorb moisture, leaving your body to overheat and sweat while in bed,” said Tattersall.
“You know that sinking feeling you get when you sleep on a memory foam mattress? For that to happen, it needs body heat to warm it up, which is then reflected back onto you as you sleep.
“Overlaying your memory foam mattress with a wool mattress protector will help regulate around 75 per cent of that heat, helping you stay cooler on those hot summer evenings.”