Black menstrual blood is caused by low menstrual flow, prolonged retention in the vagina and pelvis, and poor discharge. 4. The poor psychological state of women, often in a depressed and nervous state, leads to abnormalities in the internal secretion system, thus affecting the inflammatory color of menstrual blood. 5. When women have kidney deficiency, they are also prone to black menstrual color, accompanied by tinnitus, dizziness, lumbago and other symptoms. If the color of menstruation continues to be black, it is recommended to go to the hospital for a timely examination.