If you’ve ever noticed lighter patches or strange discoloration on your underwear after washing, it might seem like a detergent issue—but it’s actually something natural from your own body.

Many women experience this and don’t realize the cause. According to an OB-GYN known as “The Vag Doc,” the effect comes from the natural acidity of vaginal discharge, not from anything going wrong.

The vagina maintains a healthy balance of bacteria, mainly lactobacilli, which create an acidic environment. “When your vagina is working as it should, it has a specific pH balance that includes lactobacilli and other bacteria,” she explained. This acidity helps protect against infections and keeps the vaginal microbiome stable.

That same acidity can also affect fabric. “If your discharge is more acidic, it can actually strip the dye from your underwear, leaving behind lighter patches,” she said. Over time, this creates the “bleaching” effect many notice.

The important part: this is completely normal. “A normal, healthy vagina can sometimes cause discoloration in underwear, so there’s no need to panic,” she reassured. It’s often a sign your pH is balanced and healthy.

Some women never notice this change, and that’s normal too. “Some people just have less acidic discharge than others, and that’s as well normal.” Fabric type, color, and dye also play a role in whether the effect is visible.

However, not all changes should be ignored. If discharge develops a strong odor, unusual color, or different texture, it may signal an infection. In those cases, it’s best to seek medical advice.