The causes of dark brown color on the first day of menstruation may be endometrial shedding during menstruation, cervical adhesion and endocrine disorders. 1. Shedding of the uterine lining during menstruation: A woman’s endometrial shedding during menstruation will be accompanied by mucus from the cervix, so it may appear dark brown. 2. Cervical adhesion: If the patient suffers from cervical adhesion, it may cause the menstrual blood to stay in the uterus for too long and appear oxidized and darkened, which in turn leads to dark brown blood on the first day of menstruation. 3. Endocrine disorders: If a woman has endocrine disorders, because of the changes in hormone levels in the body, it may lead to thinning of the uterine lining, which may also cause dark brown menstrual blood. It is recommended that women should maintain good living and eating habits during menstruation to ensure sufficient sleep; at the same time, they should pay more attention to the warmth of the abdomen to avoid the occurrence of cold; the diet should be appropriately increased nutrition, you can drink some brown sugar water appropriately, and try to eat as little as possible of cold and stimulating food. The first day of menstruation dark brown women may also be other reasons, if the body accompanied by other obvious discomfort, it is recommended to go to the hospital for examination and clear diagnosis.