The slightly acidic environment of the vagina helps maintain its self-cleaning function
Western medicine believes that the vaginal environment is frequently unstable due to the host's metabolic products, bacterial products, and exogenous factors (sexual intercourse, douching, and other disturbances). The vaginal flora is very complex, including not only protozoa and fungi, but also many aerobic and anaerobic bacteria. These microorganisms can be divided into commensal and pathological types, all growing in a common environment, and there may be antagonistic interactions between them. Another factor affecting their growth is hydrogen ion concentration. A pH of 3.8–4.2 is conducive to the reproduction of commensal bacteria, especially lactobacilli, which are the dominant bacteria in a healthy vagina, reaching a density of 10⁵–10⁸ ml in vaginal fluid. When the vagina is infected by microorganisms, if lactobacilli are dominant and the pH is maintained at 3.8–4.2, it will not cause disease. Furthermore, lactobacilli can produce H₂O₂, which has a toxic effect on other microorganisms and inhibits their reproduction. Other bacteria such as Streptococcus lactis, Enterobacter, Proteus, Gaffkirti, and Veillonella are commonly found in the lower vagina and usually do not produce symptoms. The vaginal flora maintains a balance, preventing pathological bacteria from exerting their influence. If this balance is disrupted, the mutual restraint disappears, leading to a decrease in hydrogen ion concentration. Lactobacilli lose their dominance, allowing pathological bacteria to proliferate and causing symptoms.
Various pathogenic bacteria become pathogenic after being disrupted in a weakly acidic environment. Bacterial vaginosis is caused by a decrease in vaginal lactobacilli and the proliferation of other bacteria, mainly Gardnerella vaginalis, various anaerobic bacteria, and mycoplasma, resulting in mixed infections. Trichomoniasis is caused by Trichomonas vaginalis, a sexually transmitted infectious disease. Transmission routes include direct transmission (through sexual intercourse; 75% of the semen of partners with trichomoniasis can contain Trichomonas vaginalis) and indirect transmission (through various bath utensils, swimming pools, public toilets, or contaminated clothing and instruments). In general surveys, the detection rate of Trichomonas vaginalis is 3.56%, with some women showing no inflammatory symptoms being called carriers. Candidal vaginitis is mainly caused by Candida albicans. This fungus is also commonly found in small amounts in a normal, healthy vagina, but usually does not cause illness. It proliferates and causes disease when the body's immune function is weakened or when there is an imbalance in the vaginal flora. Therefore, it is more common in pregnant women, women with diabetes, those using immunosuppressants, and those using antibiotics long-term. It is also more likely to cause infection in warm, moist environments. Statistics show that about 10% of non-pregnant women and one-third of pregnant women are infected with this disease, but few seek medical attention due to obvious symptoms. The incidence of vaginitis caused by non-Candida albicans (such as *Candida glabrata*) increased from 9.9% in 1988 to 17.2% in 1995. Women infected with HIV are twice as likely to be infected with non-Candida albicans compared to those newly infected; women with recurrent candidal vaginitis are 2.47 times more likely to be infected with non-Candida albicans than with Candida albicans.