Physiological cycle refers to a woman’s menstrual cycle, which is obtained by counting the time between the first day of each menstrual period and the first day of the next. The cyclical shedding of the uterine lining and bleeding that accompanies the ovarian cycle is called menstruation. The average menstrual cycle lasts from 21 to 35 days, with an average of 28 days, and a period of 21 to 35 days, plus or minus 7 days, falls within the range of a normal menstrual cycle. The length of the menstrual cycle varies from person to person and is influenced by genetic factors as well as other factors. If the menstrual cycle is often shortened, it may be caused by a decline in ovarian function; if the menstrual cycle is often lengthened, it may be caused by polycystic ovary syndrome; if the menstrual cycle is not regular and manifests itself as irregular vaginal bleeding, it may be due to organic problems, such as endometrial polyps and ovarian tumors. If the menstrual cycle is longer than 35 days or shorter than 21 days, it is an abnormal menstrual cycle and requires active medical treatment.