If you’ve ever pulled a pair of underwear out of the laundry only to notice strange light patches or discoloration in the fabric, you’re not alone. Many women have experienced this odd phenomenon, but few realize what’s actually causing it.

While it’s easy to assume your washing machine or detergent is to blame, the real culprit is something completely natural—your own body.

According to a female obstetrician-gynecologist who goes by “The Vag Doc” on TikTok, this so-called “bleaching” effect is caused by the acidity of vaginal discharge.