Studies have shown that underarm skin actually absorbs very little aluminum—only about 0.01 percent. But what about when you shave your armpits, then apply a swipe of antiperspirant? The absorption rate of aluminum goes up to 0.06 percent on pre-damaged skin, and a 2017 retrospective study "showed an earlier age of disease onset in breast cancer patients that had used aluminum-containing antiperspirants combined with underarm shaving."