If you’ve ever noticed light patches on your underwear, it’s not your detergent—it’s your body. According to a gynecologist on TikTok known as The Vag Doc, this “bleaching” effect comes from the natural acidity of vaginal discharge.

“When your vagina is working as it should, it has a specific pH balance that includes lactobacilli and other bacteria,” she explained. “This acidity is essentially what helps keep your vaginal microbiome in check.” The same acidity can “strip the dye from your underwear, leaving behind lighter patches.”

The good news: “A normal, healthy vagina can sometimes cause discoloration in underwear, so there’s no need to panic,” she said. It’s actually a sign of balance, not a problem.

Some women asked why they’ve never seen bleaching. The doctor reassured them: “Some people just have less acidic discharge than others, and that’s as well normal.” Fabric type and dye also affect whether bleaching shows.

Doctors do warn, however, to seek help if discharge suddenly changes in odor, color, or texture. But for bleaching alone? As The Vag Doc summed up, “It’s just science at work.”