So, you’ve managed to get the stains out—but how do you avoid them going forward? The key is in your deodorant, Harris tells mbg.
“Pit stains are actually typically caused by a reaction of sweat to chemicals in antiperspirant, particularly aluminum,” she explains.
The solution? “To avoid pit stains, use aluminum-free antiperspirants/deodorant, and let deodorant dry completely before putting on a shirt,” Harris notes.