"Think about cotton," says Dweck. "It's susceptible to mould and bacteria."
That's why proper storage is key. Heat and moisture can make it easier for germs to take hold and multiply. Yet most of us keep our stash in the bathroom, where the shower sets the perfect hot, wet breeding ground.
"If your bathroom is particularly steamy, you might want to think about storing them in a cool, dark cabinet instead," says Dweck.
If mould does infiltrate a tampon and you unwittingly insert it (the mould would be dark black, blue, or green, but you might not see it if the tampon is hidden by the applicator), don't freak out too much.
"You might notice itching and irritation, or increased discharge because the vagina is trying to maintain its natural pH," says Dweck.
Bacterial interlopers can similarly disrupt the natural bacterial balance in your vagina and can even cause infection, but you probably don't need a course of antibiotics to treat it unless the symptoms worsen after you've removed the offending out-of-date tampon, says Dweck. If that happens, book a visit with your gynaecologist.
Common sense rules here. Since expiry dates are marked on every tampon box, "read labels just like you would for salad or juice," says Dweck.
If you reach for a tampon and notice it's outlived its shelf-life, it's safe to use it while you run to the store for a new box. As for that emergency tampon in the bottom of your bag (because who knows how long it's been in there?): Worry less about age and more about the integrity of the wrapper and applicator. If a stray pen or hair clip has torn the protective covering, the tampon can be exposed to dust, ink, makeup, and other infection-causing bacteria that can irritate your nethers, says Dweck.
This article originally appeared on Women's Health US