Why We Get Sweat Stains—And What You Can Do About Them

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If sweat is colorless, why does your favorite white T-shirt get those unfortunate yellow armpit stains after a long day spent under the sun? As the Sci Show’s Hank Green explains in the video below, perspiration itself isn’t the culprit; it’s actually the aluminum chloride in your deodorant, which works to plug up sweat glands but inadvertently causes a yellowing chemical reaction.

Humans have two main types of sweat glands: eccrine sweat glands, which cover nearly the entire body, and apocrine sweat glands, which cover your scalp, underarms, and other hairy parts. Apocrine glands produce a thick type of sweat that's packed with fats and proteins. These molecules react and produce fiber-altering compounds when they come into contact with aluminum chloride. (The jury’s still out on why this reaction yields yellow stains, but some experts think that aluminum chloride might glue the proteins in sweat to your clothing.)

You don’t have to go deodorant-free (and lose all your friends in the process) to achieve a stain-free wardrobe. Try using an aluminum-free deodorant or waiting a few minutes after application before putting on a shirt. And in worst-case stain-arios, try enzyme-boosted laundry detergent, which can break down proteins and potentially save your shirts.

Learn more fashion-based chemistry facts by watching the video below: