The first day of menstruation, the color of black, the main reasons are as follows: First, the endometrium in the beginning of the shedding of shedding less, so less bleeding, menstrual blood in the uterus to stay a long time, there will be the symptom of the color of black, belong to the normal body reaction. Secondly, it may be the symptoms of uterine cold, if you do not pay attention to keep the abdomen warm before menstruation, the invasion of cold will directly affect the discharge of menstrual blood, resulting in the appearance of black color and other symptoms. Third, there may be bad habits, eating habits and mental factors and other issues, long-term depression or psychological pressure, may affect the discharge of menstrual blood, menstrual blood color black, menstrual cramps and other symptoms, it is recommended to usually observe the color of the menstrual blood, if the darker symptoms are more obvious, it is best to go to the hospital in a timely manner to regulate the treatment.