1. Physiological cycle: After entering puberty, women's ovaries begin to periodically secrete estrogen and progesterone, and the periodic changes in these hormones lead to periodic changes in the endometrium as well. When estrogen and progesterone retreat, the endometrium loses the support of hormones and sheds blood, forming menstruation.
2. Maturity of the reproductive system: Menstruation is one of the signs of female reproductive system maturity, indicating that women have the ability to conceive. Through menstruation, the female body is able to regularly clear the aging endometrium, preparing for the next pregnancy.
3. Genetic and individual differences: The start time, cycle length, and menstrual volume of menstruation are all influenced by genetic factors, and there are also individual differences among women. These differences make every woman's menstrual experience unique.