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Why stinky sweat is good

JUANA SUMMERS, HOST:

As cities like Pheonix find new ways to adapt to the heat, let’s talk now about how our own bodies have evolved to cool us down. We are talking sweat. In addition to its cooling effects, it turns out that sweat has another function, one that’s invisible but super important. NPR’s Michaeleen Doucleff explains why stinky sweat can actually be a signal of something good.

MICHAELEEN DOUCLEFF, BYLINE: Back in college, I had an embarrassing moment. My girlfriend borrowed my backpack for a weekend trip. And when she gave it back to me, she said...

UNIDENTIFIED PERSON: Michaeleen, you must sweat a lot because your backpack stinks. The arm straps smell like onions. Ew.

DOUCLEFF: Her exact words may have been a little different, but you get the idea. As I stood there, I remember thinking, does my sweat really smell that bad?

GAVIN THOMAS: No, I don't think does. It certainly doesn't have these really stinky, odorous molecules.

DOUCLEFF: That's Gavin Thomas. He's a microbiologist at York University, and he studies sweat. He says human sweat on its own is actually pretty much odorless.

THOMAS: So most sweat is salty water.

DOUCLEFF: That's the sweat that cools you down.

THOMAS: But - and that's not what we're interested in. We're interested in this other type of sweat, which is produced in our underarms.

DOUCLEFF: This other type of sweat contains not just salty water but also a whole cornucopia of molecules, oils, proteins and fats. The bacteria living on our skin eats some of these compounds, and they're the ones that stink. Thomas and his colleagues have found one species of bacteria in particular called Staphylococcus hominis generates a very pungent odor.

THOMAS: We've had people describe it as kind of a oniony smell. I mean, a cheesy, oniony smell. They do smell pretty bad.

DOUCLEFF: So it's this little critter that made my backpack smell like onions. OK, now, before you start scrubbing down with antibacterial soap, there's something you need to know. These bacteria are really good for you and your skin.

RICHARD GALLO: Without them, you're in trouble.

DOUCLEFF: That's Richard Gallo. He's a dermatologist at the University of California, San Diego. He and his colleagues have found that these bacteria actually help protect our skin from problems like eczema. And they also...

GALLO: They basically make a type of antibiotic.

DOUCLEFF: Which kills some dangerous microbes that can make you really sick. Gallo and his colleagues have also found that your body itself makes anti-microbial molecules and puts them inside your sweat. Mix all of that together and...

GALLO: Sweat is a - almost like an antibiotic juice. Then as the water evaporates, those antibiotics actually increase in concentration.

DOUCLEFF: So the next time you're hot, sticky and maybe a little stinky, before you towel off, thank your sweat, and the bacteria that eat it, for helping to keep your skin safe and healthy.

Michaeleen Doucleff, NPR News.

(SOUNDBITE OF SONG, "GIVE UP THE FUNK (TEAR THE ROOF OFF THE SUCKER)")

PARLIAMENT: (Singing) We want the funk. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Michaeleen Doucleff, PhD, is a correspondent for NPR's Science Desk. For nearly a decade, she has been reporting for the radio and the web for NPR's global health outlet, Goats and Soda. Doucleff focuses on disease outbreaks, cross-cultural parenting, and women and children's health.