Waking up hot at night, damp, with the duvet on the floor and a pillow that feels like a radiator, usually has an ordinary cause. Your body needs to drop its core temperature by a degree or so to fall asleep and stay asleep, and it does that mainly by pushing heat out through the skin. Anything that traps that heat, from a winter duvet to a memory foam mattress to a bedroom radiator on a timer, makes waking more likely, especially in the lighter sleep of the early hours.
This guide runs through the common causes in roughly the order they are worth checking, then the fixes, then the smaller number of situations where night sweats are worth a conversation with a GP. It does not diagnose anything, because it cannot; but it will help you tell the ordinary from the worth-mentioning.
Why heat wakes you
Your temperature follows a daily rhythm. It falls in the evening, reaches its lowest point in the small hours, and starts to climb a few hours before you wake. Sleep is deepest while the temperature is falling and lightest as it rises. If you are already too warm when the rise begins, typically 3am to 5am, you tip over into sweating and waking.
Your body also has a limited toolkit for cooling in bed: it widens the blood vessels in your hands and feet to dump heat, and it sweats. Both need somewhere for the heat and moisture to go. Trap them under a synthetic duvet on a foam mattress and you get exactly the hot, clammy 4am waking you are reading about.
In short: You wake hot when your body cannot get rid of heat fast enough. The fix is almost always to make it easier for heat to leave, not to make the body produce less of it.
The common causes
The room
The best temperature for sleep is cooler than most UK bedrooms in winter, when central heating timers bring the whole house up to 20°C or more from 5am or 6am. In summer, a bedroom that has been in the sun all afternoon can still be 24°C at midnight. Either way, the room is the first thing to check.
The duvet and what's under you
A 13.5 tog duvet is designed for cold rooms. In a heated bedroom, or from May to September, it is far too much for many people, and a partner who runs cold can make the negotiation difficult. Fabric matters too: polyester fillings and covers hold heat and moisture; cotton, linen and wool let them through. The guide to bedding and sleep explains togs and fabrics in detail.
The mattress is the cause people miss. Memory foam moulds to you, and in doing so it wraps you in a material that does not breathe well. If you have started waking hot since changing to a foam mattress or a foam pillow, that is probably not a coincidence. A cooling pillow or topper helps some people; a pocket-sprung or hybrid mattress helps more. The mattress buying guide explains which types breathe best.
Alcohol
An evening drink widens your blood vessels, raises your skin temperature and, as it wears off a few hours later, produces a rebound of restlessness that often includes sweating. If your hot nights follow evenings with wine, the connection is real, and alcohol and sleep explains why.
Late exercise, late food, hot baths
Vigorous exercise raises core temperature for a couple of hours afterwards. A big or spicy meal does something similar through digestion. A hot bath right before bed can help you fall asleep, because the drop in temperature afterwards is the sleepy signal, but if it is too hot or too late you go to bed still warm. The guide to exercise and sleep covers timing.
Sharing the bed
Two people under one duvet produce twice the heat. Separate duvets, a Scandinavian habit that is catching on in the UK, solve more overheating (and more cover-stealing) than any product.
Hormones
Hot flushes and night sweats are among the most common symptoms of the perimenopause and menopause, and they can begin years before periods stop, often as broken sleep before anyone connects it to hormones. They are worth raising with a GP, because there are effective treatments, and the NHS has good, plain information on the options. Some people also notice a warmer phase of the menstrual cycle, and pregnancy raises body temperature too.
Medicines and illness
A fever, a cold, or some medicines, including some antidepressants, some painkillers and some diabetes medicines, can cause sweating at night. Do not stop or change any medicine because of this; mention it to your GP or pharmacist and ask.
How to stay cooler
Work down this list; most people do not need to get to the bottom of it.
- Turn the bedroom radiator down, or off. Let the rest of the house be warm and keep the bedroom cool. If the heating comes on before you get up, set the bedroom valve low.
- Drop a tog. A 4.5 tog duvet in summer, a 7.5 or 9 tog in a heated bedroom in winter. Or use a sheet and a blanket you can peel off in layers.
- Switch to breathable fabrics. Cotton percale or linen sheets and covers, a cotton or wool duvet filling, and nightwear you could wear on a warm day.
- Deal with the mattress. A breathable topper, a cooling pillow, or a different mattress type if foam is clearly the problem.
- Get air moving. A window open a crack, or a quiet fan on low. Moving air lets sweat evaporate, which is how cooling is meant to work.
- Move alcohol, big meals and hard exercise earlier, and keep the bath warm rather than hot.
- Separate duvets if you share a bed with someone who runs at a different temperature.
- Keep water by the bed and do not pile the duvet back on when you wake cold and damp; change the pillowcase and let yourself cool first.
If the problem is a heatwave rather than a nightly pattern, there is a dedicated guide to sleeping when it's hot in a UK home without air conditioning.
If your head and neck are where the heat gathers, a pillow that lets heat out, rather than a dense foam one that stores it, is often the cheapest single change. The best cooling pillows guide explains what actually makes a difference and what is just marketing.
Two changes with a big effect on a hot night
A pillow that sheds heat, and a duvet that is honest about the season.
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Gel-layer cooling pillow
Example: Various (gel-topped memory foam)
Cooling pillows commonly combine memory foam with a gel layer or gel-infused foam, and are marketed as feeling cooler to the touch. The cooling effect is usually most noticeable at first contact rather than all night.
- Best for
- Hot sleepers who like foam support
- Key feature
- Gel-infused or gel-layered foam marketed to draw heat away from the head
- Why it may help
- If you wake up hot, the pillow is one of the warmest contact points. A breathable or gel-layered pillow paired with a cool room can help.
- Worth knowing
- Cooling claims vary and are hard to compare; a breathable cover and cool room matter as much as the pillow itself.
Lightweight summer duvet (around 4.5 tog)
Example: Various UK brands
Tog is the UK measure of a duvet's warmth. Duvets around 4.5 tog are marketed as summer weight; all-season sets combine a summer and a mid-weight duvet that clip together for winter.
- Best for
- Hot sleepers and UK summers
- Key feature
- Low tog rating for minimal insulation
- Why it may help
- Swapping a 13.5 tog winter duvet for a summer weight one is one of the simplest ways to stop waking up hot.
- Worth knowing
- Fill (down, feather, microfibre, wool) affects breathability as much as tog.
When night sweats are worth a GP visit
Most hot nights are the room, the bedding or the drink, and they stop when you change those. A smaller number are worth checking. Make an appointment if:
- your sweats are drenching, soaking nightwear or sheets, most nights, in a cool room
- they have started recently with no obvious change in your bedroom or habits
- they come with unexplained weight loss, a fever, a cough, swollen glands, or feeling generally unwell
- you think they may be linked to the menopause and are affecting your sleep or your days, since treatment is available
- you have started a new medicine and the sweating began with it
- you also snore loudly, wake gasping, or feel exhausted however long you sleep
A GP can look for the treatable causes, which include hormonal changes, thyroid problems, infections, low blood sugar and, rarely, more serious conditions. The point of going is not to worry; it is that the common causes are easily managed and the uncommon ones are better found early. There is a broader guide to when to see a GP about sleep, and the rest of the Waking at Night guides cover the other reasons you might be surfacing in the early hours.
The short version
Cooler room, lighter duvet, breathable fabrics, air moving, alcohol earlier or gone. Check the mattress and pillow if they are foam. If the sweats are drenching, new, or come with other symptoms, see a GP. Tonight: radiator down, window cracked, one layer off.
Frequently asked questions
Why do I wake up hot at night but feel cold when I get up?
Because you have been sweating. Your body heats up under the duvet, sweats to cool down, and then the damp skin and bedding chill you once you throw the covers off or get up. Lighter, breathable bedding that lets heat out before you reach the sweating point usually stops the swing.
Is waking up sweating a sign of something serious?
Usually not. A warm room, heavy bedding, alcohol, spicy food, exercise late in the evening and the menopause are far more common causes. Sweats that are drenching, happen most nights regardless of the room, or come with weight loss, fever, a cough or swollen glands should be checked by a GP.
What temperature should my bedroom be?
Cooler than most people keep it. Around 16 to 19°C suits most adults, and the heating is often the culprit in UK homes in winter: a boiler timed to come on at 5am can wake you at 5am. Turn the bedroom radiator down and let the duvet do the work.
Sources and further reading
- NHS: Night sweats
- NHS: Menopause
- Sleep Foundation: The Best Temperature for Sleep
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Written and reviewed by the Quiet Mind Sleep editorial team in line with our editorial policy. Spotted an error? Let us know.
