It's often one of the last items of clothing we replace, which is why a TikTok video claiming women should throw out their underwear every six to nine months had people understandably worried.
But experts have since come forward to rubbish the claim, with one gynaecologist telling news.com.au the implication from the viral video that "bacteria, pathogens and fibres" in old undies aren't destroyed by washing machines is simply not true.
"From a health perspective, there is no need to throw out your underwear every six to nine months, provided you're wearing a fresh pair every day and you're washing them in a hot water wash after every wear," Dr Shreya Andric, a Sydney-based specialist dermatologist, told news.com.au.
"It is true that washing machines may not kill all the organisms, however, there is a phenomenon called 'the inoculum effect' whereby it takes a certain amount of organisms to cause an infection.
"Your washing machine will not leave behind enough bacteria to cause a problem for you."
Medical experts were forced to speak out after US woman Casaundra, who calls herself the @kittychemist and sells her own line of feminine hygiene products via TikTok, went viral with her underwear claims.
"Not all bacteria, pathogens and fibres can removed during washing," she claimed.
Casaundra also said she had previously caught "an infection from my underwear" after keeping them for too long.
"The longer we keep our panties, the higher the chances that the bacteria pathogens and particles of you-know-what [faeces] can stay on your underwear," she said in another video.
Casaundra's claims sparked a furious debate on TikTok, with many women claiming it simply wasn't feasible or necessary to replace your underwear that often.
"Yeah no sorry I'm broke," one person commented.
"I don't know what bacteria you're talking about but I've kept underwear for years and I've never had a yeast infection or UTI," another woman wrote.
Soon medical experts were weighing in, with Canadian gynaecologist Jennifer Gunter rubbishing claims that underwear needed to be replaced so often.
Gunter is the author of The Vagina Bible and is famous for debunking questionable female sexual health treatments, such as the use of jade eggs.
In her own TikTok video, Gunter said it was "simply not the case" that underwear became "some type of infectious catastrophe" at the six-month mark.
"When people tell you that you need to do really special things with your underwear, that's just an extension of purity culture," she said, referring to the belief that women should stay 'pure' and not have sex before marriage.
"It's not true at all, you should wash your underwear like you wash other things that touch your body, but they don't magically become an issue at six to nine months."
Gunter also shared a pair of her own underwear, which was older than six months and told women to buy new underwear "when you want to or it falls apart".
"The only thing that you see with it is the gusset has a little bit of bleaching because vaginal discharge is acidic and if you wear black underwear you're going to see it," she said of her underwear.
Andric agrees, telling news.com.au the only time to ditch your undies is if they are damaged or too tight.
"Replace your underwear when they become frayed, the elastic stops working, and they are no longer supportive.
"Also, underwear that is too tight can cause vulval and vaginal irritation and potentially infection so if the fabric has shrunk or your body has changed shape then it's time to say goodbye."