When the discharge is yellow and suddenly comes back to red, it may be related to the onset of menstruation, uterine cavity infection, intrauterine residue, and so on. 1. The onset of menstruation: Normal menstruation can appear after the discharge of yellow discharge, if the bleeding is heavy, accompanied by lower abdominal pain or lumbago, and the bleeding is cleared in 3-7 days, it is considered to be the normal onset of menstruation. 2. Intrauterine infection: If the uterine cavity is infected by bacteria, it will also lead to yellow and red discharge, and will be accompanied by different degrees of pain in the lower abdomen, lumbago and discharge odor and other symptoms. 3. Intrauterine residue: Postpartum intrauterine tissue residue can also lead to yellow and red discharge, usually accompanied by pain in the lower abdomen, flesh-like tissue discharge, or foul smell. In addition to physiological factors, it is necessary to actively go to the hospital to consult a doctor.