Body odor can vary from person to person, though, and some people tend to have more onion-y sweat than other people. It turns out there's a scientific reason why "onion" pops up as a descriptor. According to NPR, when your armpit bacteria gobble up your sweat, they turn the odorless human sweat molecules into other products called thioalcohols.
While pure human sweat is completely odorless, these specific compounds produced by the bacteria are definitely not. They smell really distinct — like rotten eggs, onions, or meat (hungry yet?). The reason for the similarity to onions, though, is because actual onion scent is also caused by thioalcohols (via Journal of Food Science). You will also, interestingly, find thioalcohols in skunk spray (via Gizmodo).
So, while you may be glad to know that smelling like an onion is totally normal, you still might not be super thrilled to do so. Slap on some deodorant and maybe the onion smell will stay away.
