1.Vulva: the skin of vulva is squamous epithelium, which has strong ability to resist infection. The labia majora on both sides are naturally closed to cover the vaginal opening and urethral opening to prevent contamination by external microorganisms. 2. Vagina: Normally closed, the front and back walls of the vagina are close together, and the mucin in the physical vaginal secretions forms a barrier to reduce the invasion of outside microorganisms. Lactobacillus in the vagina maintains the normal acidic environment of the vagina and inhibits the growth of other pathogens, which becomes the self-purifying effect of the vagina. 3.Cervical: The inner cervical opening is tightly closed and secretes a lot of mucus to form jelly-like mucus plugs. The mucous membrane of the cervical canal forms a lot of folds to increase the surface area of the mucous membrane and inhibit bacteria from invading the endometrium. 4.Endometrium: The cyclic shedding of endometrium can eliminate intrauterine bacteria. 5, Fallopian tubes: The cilia of the mucosal epithelium of the fallopian tubes swing in the direction of the uterine cavity as well as the peristalsis of the fallopian tubes, which helps to stop the invasion of pathogens and to remove pathogens that enter the fallopian tubes by chance. 6. The immune system of the reproductive tract. Causes of gynecological inflammation 1. destruction of natural defense function; 2. decrease of body immunity; 3. endogenous flora dysbiosis; 4. invasion of exogenous pathogenic bacteria.