A deodorant is a substance applied to the body to prevent body odor caused by the bacterial breakdown of perspiration in armpits, feet, and other areas of the body. A subgroup of deodorants, antiperspirants, affect odor as well as prevent sweating by affecting sweat glands.
Your sweat doesn’t actually smell, it’s when it mixes with the bacteria on your skin that it releases an odour. Your armpits and pubic regions contain thousands of hairs which then hold on to your sweat and the bacteria.
When you swipe a stick of deodorant against your armpits in the morning, you’re doing more than just masking bad odors with a flowery fragrance. Reactions, a video series from the American Chemical Society, breaks down the chemistry of smelly pits and how deodorant and antiperspirant fight odor by knocking out bacterial function.
There are one million bacteria per square inch on your pits, and when they go to town on the fats and proteins secreted by your skin when you sweat, they produce chemicals that smell like onions, cumin, and regular ol’ B.O. Deodorants contain chemicals that kill or block those bacteria, stopping them from producing smelly chemical byproducts. Some deodorants contain triclosan, for instance, a chemical that makes the armpit too salty for bacteria to live. Antiperspirants, on the other hand, plug up sweat glands with aluminum salts, preventing that smelly reaction from occurring.
But before you go salting the fields of your bacteria-rich armpits, there is actually a defense for going au naturale. Some contend that before regular showers and Old Spice, certain bacteria living on our skin may have kept us from smelling too bad. Some companies even sell bacterial concoctions that purportedly reduce your need for deodorant at all—though we won’t try to take an official stance on how well they work.