A woman’s endometrium sheds to menstruate because of the cyclical changes in the hormones in her body. From the beginning of menstruation, the estrogen level in the body starts to rise gradually, causing the endometrium to proliferate and cover the entire uterine cavity, and menstruation ends. After ovulation, the level of progesterone in the body also rises, causing proliferation in the interstitial part of the woman, when the endometrium does not grow abnormally long, and progesterone and estrogen have an antagonistic effect. When the level of estrogen and progesterone in the body suddenly decreases 2-3 days before menstruation, the endometrium loses its hormonal support and sheds, accompanied by bleeding, shed cervical cells, shed vaginal cells, and cervical mucus discharge, resulting in menstruation.