Finding light or “bleached” patches on underwear can be surprising — and sometimes worrying — but in most cases, it’s completely normal and harmless.

For women, the most common cause is natural vaginal discharge. The vagina has a naturally acidic environment, which helps protect against infections and maintain healthy bacteria. This acidity can gradually lighten or discolor fabric, especially darker underwear, creating what looks like bleach stains. It’s actually a sign that the body’s natural defenses are working as they should.

Hormonal changes, ovulation, pregnancy, or increased discharge can make these patches more noticeable at certain times of the month. The effect varies from person to person and can also depend on fabric type and dye quality.

For men, lighter patches may come from sweat, skin oils, or natural bodily fluids, which can also affect fabric dyes over time — especially with tight clothing or prolonged wear.

In most cases, these changes are not related to hygiene and don’t indicate a health problem. However, if discoloration is accompanied by strong odors, itching, burning, unusual color changes, or discomfort, it may be a sign of infection and should be checked by a healthcare professional.

Bottom line: those “bleach” marks are usually just chemistry at work — a normal interaction between the body and fabric — and nothing to be alarmed about.