There are two types of yellow discharge on the underwear, one is physiological yellowing and the other is pathological yellowing. Physiological yellowing is caused by the exuberance of estrogen and progesterone after ovulation, which may cause more shedding cells and may result in milky white or yellow discharge. Yellow discharge immediately after menstruation indicates vaginal inflammation. It is recommended to go to the gynecology department for vaginal discharge examination to determine whether it is trichomoniasis or bacterial vaginitis. As far as possible, you should change your underwear every day in your future life, and disinfect them by boiling water and sunlight.