Menstruation, which is bleeding caused by the endometrial lining peeling off. A woman’s ovaries produce eggs, as well as secrete sex hormones. The eggs in the ovaries grow, develop and are discharged periodically, and the eggs are discharged to form the corpus luteum. At the same time, the endometrium is affected by the estrogen and progesterone secreted by the ovaries and undergoes cyclic changes. The estrogen secreted by the ovaries can cause the endometrium to gradually thicken. After ovulation, the endometrium is further thickened by the influence of progesterone. About 14 days after ovulation, the corpus luteum atrophies, estrogen and progesterone secretion sharply decreases, the blood vessels in the endometrium contract, the endometrium becomes necrotic and sheds, which causes bleeding and the formation of menstruation. Menstruation is a physiological characteristic of women, and such cyclical changes usually occur once in about 28 days. During menstruation, it is important to take care of your period by resting and keeping warm.