During menstruation, women’s body functions are relatively lower than usual due to changes in hormone levels, and a small number of women experience diarrhea. Diarrhea is mainly caused by pelvic congestion and pressure on the rectum during menstruation, which can cause irritation. It may also be caused by eating unclean food during menstruation due to a decrease in body resistance and immunity. During a woman’s menstruation, her body releases a hormone called prostaglandin. This hormone not only stimulates the uterus, causing it to contract and expel menstrual blood, but also stimulates the intestines to increase their contraction and peristalsis, which can easily lead to mild diarrhea symptoms. Therefore, if the symptoms of diarrhea are not very serious, it is actually a physiological phenomenon of the body. In this case, no special treatment is needed and it will recover on its own after the menstruation. On the other hand, during menstruation, the pelvic cavity becomes engorged with blood and the uterus enlarges accordingly, thus compressing the rectum and causing an increase in the number of stools. The above two cases of diarrhea belong to a physiological phenomenon during menstruation, but if the diarrhea is accompanied by high fever, vomiting, severe pain in the abdomen and a series of other phenomena, it is a pathological phenomenon and requires timely treatment in the hospital.