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The importance of sweat: We need it to keep cool

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NPR begins a celebration of sweat — what it's made of, where it comes from and what it smells like. Spoiler alert: most of the time it doesn't have any smell at all.

LEILA FADEL, HOST:

Today, NPR begins a celebration of sweat - everything you wanted to know about sweat but were too hot to ask. Our science desk explores sweat science as a public service. NPR's Joe Palca kicks things off.

JOE PALCA, BYLINE: When my editor asked me to do this story, I said, no sweat. First, let's talk about what sweat is. The human body is basically a bag of liquid with a few bones and organs thrown in to make things interesting. Some of that liquid is in arteries and veins, but some of it is in the interstices, the spaces between cells and bones and organs. And it's that interstitial fluid that's critical to understanding sweat. Why? - because sweat...

LINDSAY BAKER: Comes from the interstitial fluid in your body, so that's the starting point.

PALCA: That's Lindsay Baker of the Gatorade Sports Science Institute. Yeah, that Gatorade. She's forgotten more about sweat than most people will ever know. I keep wanting to call her the sultan of sweat, but it's a bit of an obscure joke. Baker says sweat is released from special glands in the skin called ecrine glands.

BAKER: We have about 2 to 4 million glands across our body surface. And this ecrine sweat is composed mostly of water and salt.

PALCA: So that's what sweat is - basically just salt and water from the spare liquid sloshing around in your body. Question two, why do we sweat? We sweat to keep cool. When sweat evaporates, it cools the skin, and it cools the blood and the blood vessels near the skin. The cooler blood flows to the rest of the body, and we avoid overheating. Question three, does sweat stink? Surprising answer, mostly no.

STEVE XU: Ecrine sweat is in large part pretty odorless.

PALCA: Steve Xu studies sweat at Northwestern University. But, in fact, there is a stinky form of sweat. In addition to ecrine glands, Xu says there's something called apocrine glands.

XU: They kind of exude a certain more protein-rich sweat.

PALCA: And these apocrine glands are found mostly in the groin and armpits. Apocrine sweat contributes to the fragrance of compounds emanating from those areas. So there you are. Sweat - it may smell a bit, but we really need it to keep our cool.

Joe Palca, NPR News.