It's summer and people are hot. We answer some questions about sweat As part of our summer series on sweat, we get answers to the questions: Do we need to sweat during sleep? And, why does a warm bath help you sleep, even if it makes you sweat?

It's summer and people are hot. We answer some questions about sweat

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It's summer, it's hot, and so people are sweating. The NPR Science Desk has taken it upon itself to explain the science of sweat. Today, NPR's Joe Palca tells us about sweat and sleep.

JOE PALCA, BYLINE: People sweat when they exercise. Exercise warms the blood. Evaporating sweat cools the blood. The body temperature stays just right. When you sleep, there is no exercise, so do people really need to sweat when they're asleep?

ED HARDING: Yes, they do.

PALCA: Ed Harding studies sleep and temperature regulation at the University of Cambridge. Turns out our bodies want to be cool while we're sleeping.

HARDING: We are sort of hardwired, if you like, to have a lower temperature during sleep than we do during wakefulness.

PALCA: That means you could start sweating while you're asleep if you're under too many blankets because your body wants to stay cool, man.

HARDING: If you're overheating, what's going to happen is you sweat a lot. Then you take off the bedding, and now you're freezing. And you wake up literally in a cold sweat.

PALCA: Now you know why that can happen. And here's a fun fact. Harding says it helps to take a warm bath before going to sleep.

HARDING: At face value, it seems quite paradoxical.

PALCA: But remember, your body wants a lower temperature during sleep than during wakefulness. And a warm bath actually helps you cool off, at least after you get out. The water on your skin evaporates, just like sweat would, cooling the blood vessels near the skin and cooling your body. It does take a while for the cooling to occur.

HARDING: If you try to sleep immediately after your bath, that's not going to work.

PALCA: But if you wait a bit, maybe an hour, you'll be rewarded.

HARDING: You will fall asleep quicker. And actually, if you measure the EEG, you sleep deeper.

PALCA: How about that? Some news you can use from the NPR Science Desk's summer series on sweat.

Joe Palca, NPR News.


C+C MUSIC FACTORY: (Singing) Come on let's sweat, baby. Let the music take control.

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