There are many reasons why a woman’s menstrual blood may be dark in color. It may be caused by just bad living and eating habits, or it may be caused by organic gynecological diseases. If the menstrual blood is not discharged smoothly due to cold invasion within a week before or during the menstrual period, it will cause the menstrual blood to be dark in color. All factors that affect the timely discharge of menstrual blood may lead to black menstrual blood. 1. cold invasion of the uterus, low ambient temperature, too cold diet, rain, cold water bathing, etc., may lead to cold invasion of the uterus, causing black menstrual blood; 2. excessive smoking and drinking, often a large number of high-fat diet, resulting in hardening of the blood vessel wall, increased blood viscosity, slow blood flow, affecting the normal discharge of menstrual blood The endometrium loses its normal response to the action of estrogen and progesterone and cannot proliferate and exfoliate normally, thus causing the dark color of menstrual blood.