Underwear needs to be changed regularly to avoid becoming a breeding ground for bacteria. Chest and critical care specialist Dr. Huang Xuan noted that studies show even with regular washing using laundry detergent, intimate clothing can still retain an average of 0.1 grams of fecal particles per item, often containing E. coli and other bacteria. He recommends replacing underwear and bras every 3 to 6 months and washing them in water above 60°C or drying them under sunlight to effectively kill germs.
Dr. Huang explained on his Facebook page that U.S. research analyzing household laundry found that bacteria can persist even after standard washing. The washing machine drum itself may also harbor microbes, causing recontamination of clean clothing. In warm and humid conditions, this can lead to repeated irritation, infections, or urinary tract inflammation.
According to guidelines from the Japan Society of Obstetrics and Gynecology and the Japanese Association for Infectious Diseases, women’s intimate wear should be replaced every 3 to 6 months. Over time, fibers absorb sweat and secretions, making it difficult to fully eliminate bacteria even after washing, increasing the risk of recurrent yeast infections and bacterial vaginosis. Underwear used beyond six months also loses elasticity, allowing bacteria to cling more easily, and high-temperature washing may not fully sterilize it.
Dr. Huang emphasized that underwear should be replaced regularly. For women, a slightly acidic vaginal environment combined with moisture and friction can trigger yeast infections. Men should avoid overly tight or non-breathable underwear, which may affect testicular temperature and sperm quality. He advises choosing breathable materials such as modal or cotton blends, changing underwear daily, and replacing old items every 3 to 6 months. Proper cleaning—washing in water above 60°C or sunlight exposure—can effectively kill bacteria.
