Menstruation is vaginal bleeding caused by the periodic shedding of the endometrium. The main components of menstrual blood consist of cervical mucus, blood that flows out when the endometrium is shed, and shed material from the endometrium. Under normal circumstances, the color should be a dark red, clot-free, odorless fluid. It is also normal for some women to have a menstrual period that is a large red color like fresh blood. This indicates that the endometrium is shed at a faster rate. If the menstrual blood is found to be light red and thinner, it may be caused by anemia. If the menstrual blood is dark red and there are many clots, it indicates that the woman has a colder constitution. There is also a condition where the menstruation is dark brown, which means that the menstrual blood does not flow smoothly. This phenomenon is mostly seen in women with cold body and irregular menstruation. If there is a lot of brown discharge in the premenstrual period, it may be caused by inflammation.