Does Your Underwear Have An Expiration Date?

Photographed by Meg O'Donnell.
Here at Refinery29, I’ve become the resident expert on underwear. How often should you change your skivvies? Should you wear panties to bed? I’m the go-to gal for these kinds of below-the-belt questions. But when my editors asked me to write about how often you need to replace your undies, I balked. I thought of my overcrowded lingerie drawer, stuffed to the brim with an assortment of thongs and boyshorts. While I bought some pairs more recently, probably half of them were paid for with coupons in college. I even have a few stray pairs from high school. (If you think I’m going to throw away the black and pink starred pair I wore before I lost my virginity, you don’t get me!) 
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When I did a quick Google search for how often I should be replacing my underwear, I was dismayed to see that the first result was from a men’s fashion blog stating the “rule of thumb” was that you should refresh your supply of undergarments every six to 12 months. I shuddered and thought: Oh my god! Am I… gross? 
But luckily for my sense of self, I pushed further in my research, and got on the phone with Philip M. Tierno, Ph.D., professor of microbiology and pathology at the New York University School of Medicine, and author of the upcoming book, First, Wear A Face Mask: A Doctor’s Guide to Reducing Risk of Infection During the Pandemic and Beyond. 
Tierno says that as long as you’re washing your underwear after every use, there’s no germ-related reason to toss out your old knickers after some arbitrary period of time. They don't have an expiration date. “As long as you’re washing and disinfecting your underwear, and they’re mechanically functional, with no holes, and they’re not soiled, you can keep those,” Tierno says. “When they become frayed or the elastic stops working, you’ll know to replace them."
To properly clean your drawers between wears, toss them in the washing machine preferably with a detergent that contains peroxide, on the hottest setting recommended on the care label.
Still, even after you wash your underwear, there will likely be some bacteria looming on the fabric —  there’s about one-tenth of a gram of poop in the average pair of “clean” underwear, 2001 research from the Journal of Infection found. But the vast majority of bacteria will be eradicated with a proper wash, and the small amount that sticks around won’t hurt you, Dr. Tierno says. 
“Washing machines may not kill all the organisms, but there’s another phenomenon, the inoculum effect, which means it takes a certain amount of organisms to cause and infection,” he says. Your machine won’t leave behind enough microbes to create a problem for you, Tierno says. If you want to be extra careful, disinfect your washing machine by running a bleach cycle with no clothes on a monthly basis, to make sure it's not collecting extra bacteria, he recommends. 
So, as it turns out, underwear are not like toothbrushes, and don’t need to be replaced cyclically for bacterial reasons. As long as you're donning a fresh pair every day, and washing them after every use, you can wear them until they’re old and dingy looking. And yes — it's fine to save older, more memorable bloomers for the odd trip down memory lane.

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