When adolescent women first have menstruation, the menstruation is brown and the amount is relatively small, mainly because the reproductive organs are not mature, the endometrium is relatively thin, the endometrium is shed to form menstruation, the endometrium is shed less, and it remains in the vagina for a long period of time, so the color of the liquid is heavy brown, 1-2 years later the reproductive organs are gradually developing and maturing, and the menstruation will gradually change to the color of blood. If a woman already has normal menstruation, the first 1-2 days of menstruation, due to the endometrial shedding less, in the vagina for a longer period of time, so it will be brown, 1-2 days later, that is, 2-3 days after the onset of menstruation, menstruation will gradually change the color to blood, and the amount of menstruation gradually increased, continued for 2-3 days of menstruation will gradually reduce the amount of menstruation to return to its original brown color. The color of menstruation will also change depending on the time of the menstrual flow.