Why Do I Get So Hot When I Sleep? What to Change

Your body has to shed heat before sleep will start.

Why do you get so hot when you sleep? Begin with what your body is trying to do. Core temperature falls at night, and that fall is part of the daily cycle your internal clock keeps. The National Institute of General Medical Sciences lists temperature among the functions that clock controls, next to sleep timing and hormone release.

Your body makes the drop happen by opening the blood vessels in your hands and feet. Warm blood comes to the surface, and heat leaves through the skin. That is why your feet feel hot as you drift off, and why cold feet keep you awake.

Researchers track this as the gap between skin temperature far from the heart and skin temperature near it. A 2011 review in Pflugers Arch reports that controlled studies put that gap forward as the best available marker of how fast sleep arrives, while studies in ordinary bedrooms have not always matched it. Heat moving out is the thing being measured either way. Anything that traps it is working against you.

Your body will make heat either way. What you can change is whether the bed lets it out. No pillow and no comforter changes your body clock, and anyone who tells you otherwise is selling. Bedding decides one thing, which is whether the heat you produce can leave. That is a smaller claim and it is the one you feel, because your body temperature during sleep is already moving whether you help it or not.

Photo: Circadian

The bed holds more heat than anything else in the room.

What in your bed is making you hot? The mattress first, then the comforter, then the pillow. Each one sits between your skin and the air, and each one either lets heat through or keeps it. The mattress is the biggest surface and the hardest to change. The pillow is the smallest and the easiest.

Memory foam is the clearest case. It is a solid block with small sealed pockets, so air does not travel through it, and it softens as it warms. Your heat stays in the dent your body made, and the dent gets warmer as the night goes on. Polyester does the same job inside a comforter. The fiber takes on almost no moisture vapor, so what your skin gives off sits right where it landed.

Method: every row above describes the published structure of the material, and the Circadian figures come from our own product pages. Nothing here was measured in a lab by us.

Cooling gels and phase-change panels sit in a category of their own. They start cold because they are colder than you, then they take on your heat until they match it, and after that they are a warm surface you cannot cool down. Tempur-Pedic and Purple build the foam version of this, and Avocado, Coyuchi and Naturepedic build with natural fiber instead.

A warm room leaves your skin nowhere to send the heat.

What temperature should a bedroom be? The Sleep Foundation puts the comfortable band at 65 to 68 degrees Fahrenheit, and calls roughly 65 the best of it. That sounds cold to read and feels right to sleep in, because your skin needs somewhere cooler than itself to send heat.

Raise the room and you shrink that gap. Your hands and feet are still opening up, and the heat still arrives at the surface, and then it has nowhere to go. Okamoto-Mizuno and Mizuno's 2012 review in the Journal of Physiological Anthropology reports that with normal covers and bedclothes, heat is what breaks a night, more than cold, in young adults as well as in older ones.

Humidity gets at you from another side. Wet air slows evaporation from your skin, so a humid room feels hotter than the thermostat says. If you have already dropped the thermostat and still wake up warm, a dehumidifier is often the cheaper next move. Our guide to the best temperature for sleep goes through the settings in order.

A partner, a drink and a prescription all add heat you did not plan for.

Why do you get hot at night when nothing in the room has changed? Usually because something outside the room did. Three causes come up over and over, and none of them are about the bed.

A second body under the same covers

A sleeping adult gives off heat all night. Two of you under one comforter is two sources under one lid, and the person on the inside of the bed gets the worst of it. This is the most common reason a bed that worked alone stops working. Two lighter comforters on one bed solve it better than one heavy one, because each person keeps their own covers and their own air.

A drink before bed

Alcohol opens the blood vessels near your skin, which is the flush you can see in a mirror. Heat leaves fast and early, and you feel pleasantly warm. Later in the night that reverses, and your body works to hold heat in instead. That is part of why the second half of a drinking night runs hot and broken. The drink did not add heat. It moved your heat forward, and the rest of the night pays for it.

Medication you take for something else

Plenty of common prescriptions raise body heat or bring on sweating as a side effect. Some antidepressants, some blood pressure drugs, thyroid medication, steroids and painkillers all show up on that list. If you got hot at night within a few weeks of starting something new, the timing is worth mentioning to whoever prescribed it. Do not stop anything on the strength of a blog post.

Hormone changes are the cause most often missed, and the one to take to a clinician.

Why do you suddenly get hot at night in your forties or fifties? Hormone change is the usual answer, and it is the cause people spend the longest trying to buy their way out of. Perimenopause and menopause bring hot flashes, and a hot flash during sleep is a night sweat. Pregnancy and thyroid conditions move temperature the same way.

The honest answer here is a person rather than a product. A clinician can tell a hormonal night sweat from an infection, a thyroid problem or a medication effect, and can treat the cause. Book that first. Bedding has a smaller job and it is a real one.

A comforter has no say in when a flash arrives. It has a say in how fast the heat from one clears. Natural fiber lets that heat move out through the covers, so the warmth passes in a few minutes rather than sitting on you until the next one. For a lot of people that is the difference between waking once and waking five times.

When a night sweat is worth a doctor's visit

Sweating heavily in your sleep, night after night, is on the list of reasons to call a provider. MedlinePlus names losing weight from sweating, or often sweating during sleep, as a reason to contact yours. Sweat that soaks a sheet, arrives with a fever, or comes with weight loss you did not intend is a symptom rather than a bedding problem. Take it to a doctor before you take it to a store.

What a pillow or comforter is made of decides how warm it gets.

Which pillow is coolest for a hot sleeper? The one whose structure lets air keep moving, which rules out solid foam and rules in the open natural fibers. Your head is a small part of your body and a large part of the problem, because your face lies right on the surface all night and there are no covers to kick off.

A wool pillow does not turn into the hot patch you keep flipping away from. Wool works on moisture vapor. The fiber takes on up to 30 percent of its own weight in vapor before the surface reads wet, so what your head gives off moves into the fiber instead of pooling at your cheek. The heat goes with it. A wool pillow suits people who wake up hot, and it suits people who run cold too, because wool works in both directions.

Choose wool if:

• You wake up hot and find the pillow warmer than the room
• You want springy, medium height rather than firm or flat
• You want the whole pillow certified organic, fill and cover together

For the sleeper who wakes up hot

Organic Wool Pillow

Your face stops landing on the hot patch. Wool moves moisture vapor into the fiber, up to 30 percent of its own weight, and the heat goes with it. GOTS, the Global Organic Textile Standard, certifies it as a finished pillow, fill and cover together, under license GOTS-10229 from Oregon Tilth.

Shop the Organic Wool Pillow

Handmade in New Jersey · Free shipping

Kapok gives you down softness that still stays cool. It works on structure rather than moisture. Each fiber is a hollow tube, 80 to 90 percent air by volume, with a wall one to two microns thick, and that is why kapok is the lightest natural fiber on Earth. Air travels through the whole pillow rather than around it. The feel stays soft and the surface stays cool, which is what anyone who gave up on down was looking for.

Choose kapok if:

• You loved a down pillow and want the same softness without the feathers
• You sleep on your back or your front and want a low, light pillow
• You want a vegan pillow that still runs cool

Down softness, from a hollow plant fiber

Wild-Harvested Kapok Pillow

Each kapok fiber is a hollow tube that is 80 to 90 percent air, so the pillow floats into a soft mound and air keeps moving through it. Gathered from seed pods on trees that are never felled.

Shop the Wild-Harvested Kapok Pillow

Handmade in New Jersey · Free shipping

The comforter is the bigger lever, because it covers more of you. A wool comforter moves vapor the way the pillow does, at the scale of the whole bed, and the Organic Wool Comforter is the one hot sleepers reach for first. The Organic Cotton Comforter is the lighter summer answer. Both are duvet inserts, so each slips inside a cover that clips at the corners and takes the wash. For the full comparison, read wool against cotton for hot sleepers.

Sheets count for less than people expect, and they still count. A 300 thread count long-staple organic cotton sheet set and a pair of pillowcases pass air freely. A polyester blend at the same count holds heat and static against you.

Five habits keep hot sleepers hot.

What do hot sleepers get wrong? The same five things, in roughly this order. The first is buying a cooling product instead of removing a hot one. A gel panel on top of a foam mattress is a cold surface on a warm block, and it is the block that decides how the night goes.

The second is fixing the pillow and leaving the comforter. Your head is a fraction of your skin, and the comforter covers most of the rest. Change the big one first.

The third is treating one comforter as a shared decision. Two people rarely want the same warmth, and two lighter inserts on one bed let each person answer for themselves.

The fourth is adding layers to fix a cold start. Feeling cold when you get in and hot a few hours later is normal, because your body is still dropping. Dress the bed for the middle of the night and use socks for the first ten minutes.

The fifth is skipping the room. A bedroom at 72 degrees undoes a lot of good bedding, and moving the thermostat down is the cheapest cool night you will ever buy.

When this advice changes

Three situations flip it. If you are cold rather than hot, a wool comforter still suits you, because moving vapor works in both directions and wool is warm without being heavy. If your heat is arriving in waves rather than steadily, the cause is often hormonal, and a clinician is the right first call. And if you share a bed with someone who runs the opposite way, stop looking for one answer and split the covers. Our pillow quiz asks about that directly.

The same question sends three sleepers three ways.

What does this look like in practice? The same complaint, three different bedrooms, three different answers.

Scenario 1: hot on a foam mattress. A sleeper runs warm on a memory foam bed and has already bought two cooling pillows. The mattress is the source. A natural fiber pillow and comforter cut the heat this sleeper can still control, and the mattress becomes the next purchase rather than this one. Start with the hot sleeper collection.

Scenario 2: hot only in the second half of the night. A sleeper falls asleep comfortably and wakes later in the night soaked. A drink with dinner, a warm room and a polyester comforter are three small causes stacking. Move the thermostat toward 65, move the drink earlier, and swap the comforter for wool.

Scenario 3: flashes rather than a slow warming. A sleeper in her early fifties gets sharp waves of heat that pass in minutes. That pattern is often hormonal, so the first call is a clinician. Bedding that lets each wave clear quickly makes the night shorter, and a wool pillow with a light cotton comforter is the pairing that does it.

A pattern Circadian sees in customer conversations

People write in about the pillow and turn out to be asking about the whole bed. A reader asks which pillow runs coolest, and four messages later we find a foam mattress, a polyester comforter and a room at 73 degrees. The pillow was the cheapest thing to change, so it got blamed. Tell us the room temperature and what is on top of you first, and you get to a cooler bed faster.

Photo: Circadian

Start with what touches you, then work outward.

So what should you change first? Work from your skin outward, and change the biggest surface you can afford to change. The comforter comes before the pillow, the pillow comes before the sheets, and the room comes before all of it because moving a thermostat is free.

Pick natural fiber at every layer you touch, and let the structure do the work. Wool moves vapor, kapok carries air through a hollow fiber, buckwheat hulls open thousands of channels, and cotton stays dense and open at once. Each one keeps the surface cool instead of warming under you. Our wool and cotton goods are GOTS Certified Organic, the standard that covers a finished textile rather than the fiber alone. License GOTS-10229, issued by Oregon Tilth, and the certifications page sets out which product carries what. Ask me for the certificate and I will send it.

If the pillow question is next, which pillow stays cooler, wool or cotton sets those two against each other, and kapok against buckwheat covers our two coolest fills.

How we checked

Every number in this article is attributed to a named source in the same sentence, and every source is linked. The physiology comes from the National Institute of General Medical Sciences fact sheet on circadian rhythms and from a 2011 review in Pflugers Arch. The sleep and heat findings come from Okamoto-Mizuno and Mizuno's 2012 review in the Journal of Physiological Anthropology, which is open access. The 65 to 68 degree band is the Sleep Foundation's published recommendation, and so is the roughly 65 degree figure inside it. The night sweat guidance is MedlinePlus, which is run by the National Library of Medicine.

The material descriptions in the table are the published structure of each fiber, and the Circadian figures are the ones on our own product pages. Nothing here was measured in a lab by us. Where a number belongs to a study rather than a product, the study is named.

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