And this time of year makes it harder. The nights are changing, but your bedding hasn't quite made up its mind. Is it still duvet weather? Is it time for the lighter blanket? Add another layer, or take one away?

You've probably tried the obvious fixes. The window cracked open. The duvet kicked off. One foot hanging out from under the covers. 

It helps, a little. But you still wake up in the small hours, too warm and wide awake.

Most of us think about the room. Fewer of us think about the layers that touch our skin for eight hours a night.

What happens to your body temperature while you sleep?

Your body holds its core close to 37°C by balancing the heat it makes with the heat it loses. At night, that balance shifts on purpose.

A 2026 review of sleep and temperature by Pierzchała and colleagues at the Medical University of Łódź explains the rhythm (Journal of Clinical Medicine):

• Core temperature peaks in the late afternoon, roughly 5–7pm.
• Falling asleep usually lines up with that temperature dropping.
• It reaches its lowest point about 2–3 hours before your usual wake-up time.
• Your hands and feet act like radiators. They have special blood vessel connections that carry far more blood than normal capillaries, so heat can move out of the body.

In short, a good night's sleep is partly a cooling process.

So why do you wake up hot?

Heat needs somewhere to go.

The same review notes that a slightly cool bedroom helps because it keeps a gap between skin temperature and air temperature, allowing heat to move away from the body.

The researchers also point out that the "microclimate" inside your bed shapes your thermal balance. That's the small pocket of air and fabric between you and the room.

This isn't about being cold. The review describes studies where small rises in skin temperature, around 0.4–2°C, actually improved sleep.

The goal is balance: warm enough to feel comfortable, open enough to let heat escape.

The research doesn't single out 3am. But it does describe a body working through the night to shed heat. If that heat is trapped, it has to go somewhere, and sweat is one of the body's ways to release it.

Is it normal to sweat at night?

Often, yes.

Its list of common causes includes:

• Menopause hot flushes
• Anxiety
• Some medicines, including certain antidepressants, steroids and painkillers
• Low blood sugar
• Alcohol or drug use
• Hyperhidrosis, a harmless condition that causes heavy sweating

The Pierzchała review adds that menopause hot flushes can break up sleep, and that in people with insomnia, hands and feet may not cool across the night the way they usually do.

The NHS advises seeing a GP if night sweats happen regularly and wake you up or worry you, if they come with fever, a cough or diarrhoea, or if you're losing weight without trying.

What does fabric have to do with it?

More than most people expect, and less than some brands claim.

A 2024 systematic review in the Journal of Sleep Research found that sleepwear and bedding materials can affect sleep by influencing skin temperature and thermal comfort.

It looked at nine studies comparing fibres such as cotton, polyester, wool, linen and down.

Some results stood out. Linen sheets improved sleep in warm conditions for young adults. Cotton is naturally breathable and absorbent, which can help manage moisture against the skin. Wool sleepwear helped people fall asleep in certain conditions. But the authors were clear that the link between fibre and sleep is complex, and that the studies were too different to compare neatly.

So there is no single "cooling" fabric that works for everyone.

A simpler layer, closest to your skin

At AIZOME, we make bedding from GOTS-certified organic cotton, dyed with plants, and we share what goes into each piece.

Cotton is naturally breathable and absorbent. When you sweat, it can take up moisture from your skin and help move it into the fabric, rather than leaving a layer of dampness against you. That matters when you're trying to stay comfortable through the night.

As the seasons change, finding the right balance can be surprisingly tricky.  Do you need another layer, or just a better one?

The fabric closest to your skin is part of that equation. Organic cotton, combined with a breathable construction and plant dyes rather than synthetic finishes, gives heat and moisture somewhere to go.

We won't tell you our sheets will stop night sweats. The research doesn't support that claim for any fabric.

What we can do is make the layer you spend a third of your life against simple and knowable.

So the next time you wake up warm, the question isn't only "Is it too hot in here?"

It's also:

"What's between me and the air?"