What is the reason for the color blackening?

Female menstrual color black, in traditional Chinese medicine this is considered qi stagnation, blood stasis caused by the phenomenon, followed by this may also be due to cold during menstruation, emotional changes caused by poor endometrial shedding. In addition to the speed of menstrual blood flow is also related, if the blood flow is slow, so that blood coagulation, it will cause color deepening.