A too-thick duvet, unbreathable bedsheets, the weather outside, hormonal hot flashes — all these are common reasons for sleeping hot at night. There are also other less obvious causes that can turn your bed into a sauna and ruin your sleep. Here are some surprising reasons why you get so hot when you sleep. 

1. Your Mattress Protector 

You absolutely need a mattress protector. As we explained in our mattress protector buying guide, a mattress protector keeps out allergens, bacteria, dirt, dead skin cells and all kinds of icky stuff that can build up in your mattress. 

But if you don't choose the right mattress protector, it can end up making you too hot and sweaty at night. 

Some mattress protectors trap heat, and can be especially uncomfortable if you already have a memory foam mattress (memory foam is notorious for trapping heat) or bedding that’s not breathable such as polyester sheets. 

Solution: All mattress protectors have a waterproof polyurethane barrier that can trap some heat. To mitigate this, cool mattress protectors add a soft layer of cotton, bamboo, silk or some other natural fabric to boost cooling and sweat-wicking. Avoid polyester mattress protectors as these tend to get hot.  

2. Your Pillow

When thinking about making the bed cooler, we mostly consider changing the mattress, bed sheets and comforter. But your pillow also matters a great deal when it comes to sleeping cool. 

A pillow that traps heat is going to make you hotter and sweatier. You’ll wake up to find yourself sleeping on a damp, smelly pillow. That’s not just bad for your comfort, it’s also unhygienic. It can cause acne and other skin problems. 

Memory foam and fiberfill pillows trap more heat than other types of pillows. It’s worse if the pillow also has a polyester pillowcase. 

Solution: Choose a cooling pillow. Some good options include latex, down and buckwheat. Shredded memory foam pillows are also cooler than solid foam ones. As for the pillowcase, go for bamboo, silk, linen or cotton. 

3. Your Duvet Cover 

You already know that your choice of comforter determines how hot or cool you sleep. And it’s not just about how thick it is, but the material as well. Natural materials like down, wool and cotton sleep a lot cooler. 

The duvet cover also matters. A synthetic duvet cover made from materials like nylon, microfiber, polyester or satin will trap heat and leave your skin clammy with sweat. 

Solution: Switch to a breathable duvet cover like the Hercleon Jax duvet cover. Natural duvet covers are the best when it comes to sleeping cool. Cotton, bamboo, silk and linen covers allow heat from your body to dissipate, helping you stay cool. They also wick away sweat.

4. An Underlying Health Condition 

Away from bedding, the reason you are sleeping hot might be inside you. We’ve written before about hormonal heat flashes and how they affect sleep during menopause. A fever can also make you sleep hotter than usual. 

There are also underlying health conditions that can interfere with your body’s cooling mechanism, making you hot no matter what kind of bedding you are using. 

Diabetes is one of these conditions. It damages blood vessels and nerves, which affects how well your sweat glands work. This can leave you feeling too hot. 

Other health conditions that can make you sleep hot include hyperthyroidism, multiple sclerosis and anhidrosis (inability to sweat).

Solution: If you get unusually hot during the day or night, no matter what kind of bedding you use, talk to a doctor. You may need to seek treatment. 

Note that some medications can also make you hot. So if you are under treatment for something, check whether it’s the medicine that’s making you sleep hot.   

5. Your Partner  

This one might hurt, but the cause of your hot and sweaty nights might be right beside you. Your body gives off lots of heat. Two bodies produce even more heat. If you are sensitive to heat, sharing your bed with someone can make you uncomfortably warm. 

Some people also give off more heat than others because of their metabolism or physiology. You might be sleeping next to a natural radiator. 

Having bedding that’s not breathable can make the problem worse because all that heat is getting trapped in the bed. 

Solution: First try to switch to cooler bedsheets (try our super breathable Jax sheets), a more breathable mattress or a lighter comforter. A cooling mattress topper made from latex or wool can also help you sleep cooler and is a cheaper alternative to replacing your mattress. 

If you get really hot, consider a bed cooling system like BedJet or SleepMe Chilipad. These systems can cool your bed to a specific temperature. 

You can also try sleeping further away from each other (no cuddles) or get a sleep divorce where you sleep separately.