Menstrual reflux is not a normal phenomenon because a woman’s normal menstrual bleeding should be between 3-7 days and is usually continuous. If vaginal bleeding occurs again when the menstrual period has ended, it is most likely caused by external environmental influences. Some of the more common ones are strenuous exercise, sexual intercourse, mood swings, cold, etc. These are the types of external environmental influences that can easily cause menstrual bleeding. Because the endometrium is relatively not very stable just after menstruation, it is more influenced by the external environment. Therefore, although this symptom is not a normal phenomenon, if it occurs occasionally, it usually does not have a major impact on the health of the body. The main thing is to pay attention to rest and not to exercise strenuously, there is usually no big problem. However, if it occurs continuously, you need to go to the hospital to check the endometrial thickness by ultrasound to know whether it is caused by abnormal endometrial thickness.