Coming blood is dark menstrual blood, which may be caused by bad living habits or due to diseases such as endometritis and uterine fibroids. 1. Poor living habits: If women do not pay attention to keeping warm before or during menstruation, do not eat well, or engage in strenuous exercise, it is easy to lead to dark menstrual blood. 2. Endometritis: this disease is mainly caused by pathogen infection, such as chlamydia, mycoplasma, anaerobic bacteria, etc., which can be infected through blood circulation transmission, lymphatic system spread and other ways. If the disease develops during menstruation, symptoms such as increased menstrual flow, prolonged menstruation and darkened menstruation will occur. 3. Uterine fibroids: the etiology of this disease is still unclear, and studies have shown that it may be related to genetic susceptibility, sex hormone levels, stem cell function mutations and other reasons. Some patients are asymptomatic, while those who are symptomatic will have symptoms such as dark menstrual blood and irregular vaginal bleeding. Dark menstrual blood may also be caused by diseases such as endometrial tuberculosis, salpingitis, and ovarian tumors. Patients should go to the hospital and undergo relevant examinations to identify the specific cause of the disease and then deal with it under the guidance of the doctor.