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.

The Science Behind the “Bleaching” Effect

In a now-viral video, The Vag Doc explained that the vagina maintains a delicate balance of bacteria, primarily lactobacilli, which help keep the area healthy. This bacteria creates an acidic environment that prevents infections and maintains overall vaginal health.

“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.”

But here’s where it gets interesting: that same acidity is also responsible for lightening or “bleaching” the fabric of your underwear over time.

“If your discharge is more acidic, it can actually strip the dye from your underwear, leaving behind lighter patches,” she said.