Normal menstrual blood is non-clotting venous blood with a relatively uniform texture. It is normal for menstrual blood to be slightly viscous, mainly due to the shedding of endometrium, which is mixed into the blood. If the texture of menstrual blood is too viscous, it is abnormal. The possible causes include the following: 1. Inflammatory secretions stimulation, when women suffer from inflammatory endometrial lesions, the inflammatory secretions and menstrual blood react with each other, resulting in changes in the color and texture of menstrual blood, manifested as dark menstrual blood, viscous texture or the formation of blood clots. 2. Dietary factors, some women have a preference for cold food, even during menstruation. If you eat too much cold food, it will affect the normal contraction of the uterus, which is not conducive to the discharge of menstrual blood, and the menstrual blood will stay in the uterine cavity for too long and become sticky and black in color.