You've probably noticed that synthetic t-shirts stink more after a workout, compared to cotton. But hey—it's not the fabric's fault. It's the microbes that hang out on synthetics, that create that characteristic stench. That's according to a study in the journal Applied and Environmental Microbiology. [Chris Callewaert et al: Microbial odor profile of polyester and cotton clothes after a fitness session]

Twenty-six volunteers—half men, half women—worked out on spinning bikes for an hour. And they did so outfitted with shirts of cotton, polyester, or a cotton/synthetic blend. Then researchers stuffed the sweaty shirts into plastic bags. The next day, a trained panel sniffed them, rating their funk. Unlucky job. Because yes—the polyester shirts were indeed more musty, sour, and ammonia-like than the cotton.

DNA analysis revealed that Micrococcus bacteria were to blame. They aren't actually all that common in the armpit itself. And they don't flock to cotton. But researchers say they thrive on the open-air lattice of synthetic fibers—where they sit chomping on the long-chain fatty acids in our sweat, turning them into shorter, stinkier molecules.

These findings might just explain one of the most vexing questions of adolescence: why do stinky shirts smell so unpleasantly different from the body odor in the armpits themselves? Could be because your favorite shirt has a microbiome of its own.

—Christopher Intagliata

[The above text is a transcript of this podcast.]