The science behind bleached underwear: It's not your laundry detergent

India Today

23-06-2025

Priya always assumed she was doing something wrong with her laundry. Every few weeks, she'd notice odd, pale patches or orangish-white stains forming on her darker-colored underwear, the fabric almost looked bleached. "I even changed my detergent three times," she laughs. "I thought maybe I was using too much soap."It wasn't until a candid late-night conversation with friends that she discovered she wasn't alone - and more importantly, it had nothing to do with poor washing habits. In fact, those faded spots are a sign of something natural, healthy, and surprisingly scientific: your vagina's pH level.advertisementWHAT IS CAUSING THOSE MYSTERIOUS BLEACH-LIKE STAINS?The discoloured or "bleached" spots that often appear on underwear - especially dark-colored ones - are caused by vaginal discharge. More specifically, they result from the natural acidity of the discharge interacting with fabric dyes and materials. According to a 2020 review in the Journal of Lower Genital Tract Disease, the average vaginal pH in healthy individuals ranges between 3.8 and 4.5, making it as acidic as black coffee or tomato juice. This acidity plays a crucial role in maintaining a balanced vaginal microbiome by preventing the overgrowth of harmful bacteria and yeast.
But what keeps the vagina acidic in the first place? The main contributor is lactic acid, produced by beneficial bacteria known as Lactobacilli. These bacteria help ward off infections and maintain the vagina's self-cleaning ecosystem.WHAT EXPERTS SAYDr. Neha Kumar, a Delhi-based gynaecologist and OB-GYN with over 15 years of experience, explains: "The acidic environment of the vagina is a sign of good health. When vaginal discharge comes in contact with underwear, the lactic acid in it can cause the fabric dye to fade, creating a bleached effect. It's completely normal and nothing to worry about - in fact, it often indicates that your vaginal microbiome is functioning well."
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WHEN IS IT NOT NORMAL?While acidic discharge is healthy, there are certain red flags to watch out for. If you notice:A foul or fishy odorGreen, grey, or chunky dischargeItching or irritationBleeding outside your periodit may be a sign of bacterial vaginosis, yeast infection, or another imbalance. In such cases, it's best to consult a doctor.SCIENCE MEETS FABRIC: WHY SOME UNDERWEAR STAINS MOREThe bleaching effect tends to be more visible on coloured or synthetic fabrics, such as nylon or spandex blends, because these materials hold onto dyes that react to acid. Cotton, especially in lighter colours, may show the effect less dramatically. A study published in Textile Research Journal (2018) explored how different fabrics respond to acids. It found that synthetic blends showed more visible colour degradation when exposed to weak acids like vinegar - comparable in acidity to vaginal discharge.CAN YOU PREVENT THESE STAINS?While the stains aren't harmful, here are a few ways to minimise them:Opt for 100% cotton underwear, preferably in lighter colorsAvoid tight, non-breathable fabricsUse panty liners during ovulation or when discharge is heavierWash underwear with mild, fragrance-free detergentAvoid douching or scented feminine hygiene products, which can disrupt pH levelsWHY THIS "BLEACH" EFFECT IS ACTUALLY GOOD NEWSThis staining phenomenon might feel like a laundry nuisance, but it's a small price to pay for a healthy, self-regulating reproductive system. Your body is signaling that the protective acidic barrier is doing its job. Priya, for one, has embraced science. "Now I just buy better underwear and wash it gently," she says. "I'd rather have a healthy vagina than worry about a faded spot."advertisementBleach stains on your panties are more than just a laundry quirk - they're a subtle, fascinating reminder of how your body works to protect you every day. And as Dr. Kumar says, "In most cases, those little marks are nature's way of saying, 'Everything's working just fine.'"HIGHLIGHTS FOR SHARING OR SIDEBARS:Vaginal discharge is naturally acidic (pH 3.8-4.5) and protects against infection.The lactic acid in discharge can bleach dark fabrics - it's totally normal.Sudden changes in discharge (smell, color, consistency) warrant a doctor's visit.