The structure of the external female genital organs shows that the vaginal opening is adjacent to the urethra and anus, and that the vaginal opening is the opening between the female internal genital organs and the outside world, so the female genital organs are vulnerable to external pathogenic factors. However, the female reproductive tract and organs have a relatively well-developed natural defense system in terms of anatomy and function, and therefore do not cause gynecological infections at the slightest pathogenic intrusion. This natural defense system includes: 1. The labia majora and labia minora of the female vulva meet on both sides, covering up the vaginal and urethral openings like two doors. 2. 2. The female pelvic floor has many muscular tissues. With the action of these pelvic floor muscles, the vaginal opening is normally closed and the anterior and posterior walls of the vagina are close together, thus resisting the invasion of external pathogenic factors. However, this function is weakened when the vaginal wall is relaxed in menstrual women. 3. The estrogen secreted by a woman’s ovaries promotes the thickening of vaginal epithelial cells, which increases their resistance to pathogens. In addition, vaginal epithelial cells are rich in glycogen, and in normal women’s vagina there is a bacterium called Lactobacillus vaginalis, which can break down these glycogen into simple sugars and then into lactic acid, so that the vaginal environment is acidic and the pH value is maintained at 4.2 to 5. Pathogens that are suitable for growth in alkaline environment are therefore inhibited, which is the self-purifying effect of the vagina. 4. Under the action of sex hormones secreted by ovaries, the glands of cervical mucosa can secrete alkaline mucus, forming mucus plugs that block the cervical canal and isolate it from the external environment, reducing the possibility of bacterial invasion. It has been reported that bacteria can be detected in the lower 1/3 of the cervical mucus plug, while no bacteria can be detected in the upper 2/3 of the mucus plug. This could indicate that the cervical mucus plug has an important role in preventing bacterial upstream infection. In addition, the endocervix is usually in a closed state, which can also prevent the invasion of pathogens. 5. With the cyclical changes of sex hormones secreted by the ovaries, the endometrium of women of childbearing age also undergoes cyclical exfoliation, producing menstruation. With the exfoliation of the endometrium and the discharge of menstrual blood, the pathogens invading the uterine cavity are also given the opportunity to be removed. Some epithelial cells in the mucosa of the fallopian tubes differentiate into ciliated cells, and these cilia are able to swing in the direction of the uterus, which, together with the peristaltic action of the fallopian tubes, can play a role in the removal of pathogenic bacteria that invade the fallopian tubes.