The Surprising Reason We Sleep Under Blankets, Even When It’s Hot

The weird history of sleeping under a blanket

If you ask someone why humans sleep under blankets in the first place, you’ll probably get responses such as “humans have always slept under blankets!” However, this isn’t true: for centuries, simply owning blankets, much less sleeping under them, was a luxury reserved for the wealthy.

For example, blankets were once very expensive: it was difficult to get all the thread for them, and each one was usually made by a single person rather than a machine. Accordingly, it cost so much to buy a blanket that only the ultra-rich could afford it. To give you a better idea of how valuable blankets once were, Mental Floss reports that it was once a common practice for a person’s will to stipulate who would get their blanket after they die!

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When you want that blanket, the heat doesn’t matter

The Industrial Revolution helped ensure that blankets were much easier to manufacture, and that led to almost everyone having a blanket. Over time, though, the effects of that revolution led to rising global temperatures. That’s when scientists began to notice an interesting phenomenon: as a rule, almost everyone likes to sleep under a blanket, even when it’s hot outside.

From an outside perspective, you’d expect us to reach for the sheets when we’re cold and ditch the sheets when we’re hot. But we reach for the sheets regardless of the temperature, and if you’re curious as to why, we may finally have an answer!

A dropping core temperature is one reason you reach for the sheets

The primary reason you reach for those blankets when it’s hot outside is simple. Your body’s internal temperature is separate from the environmental temperature. And from shortly before you fall asleep to the whole night you spend snoozing, your body keeps your core temperature lower than usual.

In other words, your body will make you feel cold even when it’s warm outside. And whenever we’re cold, we reach for the blankets (even if the temperature outside is hot enough to have kept us indoors for the whole day).

Your body can’t regulate its own temperature while you sleep

At this point, you might have a simple question. If we reach for the blankets even if it’s hot because our core temperature has cooled down, why don’t we simply raise our core temperature back up and be done with it? However, that simple question has an equally simple answer: we can’t!

That’s because our bodies don’t just lower core temperature for no reason…our bodies lower the temp to help with our circadian rhythms, which help our bodies know when to get to sleep and when to wake up. And once you get to the REM part of your sleep cycle, your body loses the ability to regulate temperature like it normally does, which is why we feel the need to stay warm under the blanket throughout an otherwise warm summer night.

We’re conditioned to love blankets

All of this behind-the-scenes biology helps explain the main reason we sleep under blankets, even when it’s hot. However, you might be surprised to discover there is also a psychological element to us always sleeping under blankets. In short, it’s something we have been conditioned to do all our lives!

From a very young age, children are conditioned to reach for a blanket when it’s time to go to bed. Early on, there are pleasant childhood associations with the blanket, like our parents telling us we’ll be safe under there. Over time, there is also a physical aspect of the conditioning: we enjoy how blankets trap warm air, making us feel cozy. Between the physical and mental conditioning, we just get used to always grabbing a blanket when it’s time to go to bed, no matter the season or temperature.

Incidentally, all of this adds up to the real reason why weighted blankets have become so popular, especially for those who have anxiety or general trouble sleeping. A little added weight adds the sensation of being hugged and held throughout the night, and between this and our other positive associations with sleeping under the sheets, weighted blankets can help you get an amazing night of shut-eye.