For instance, if you apply makeup with dirty hands, use your products when you're sick, share makeup with someone else, never clean it, etc. And it's not just that you’re transmitting germs to your makeup — you’re then getting that bacteria-ridden makeup in your mouth, eyes, and any broken skin.

"If you have an open cut or pimple, the dirty makeup could get in there and cause an infection like staph — or if it's your eye, it can cause irritation or conjunctivitis [pink eye]," Whittier says. And viruses like the flu or a cold — or even the herpes simplex virus — can also survive on lipsticks for days to weeks thanks to the waxes and proteins in them.

So no, contaminated makeup won't kill you, but it could cause a nasty skin or eye problem that requires a doctor's visit. Not to mention, there might be poop in your old makeup, too. "After three months, makeup will probably also have some fecal matter since it's usually stored and used in the bathroom next to the toilet," Whittier says. Fantastic.