Normal vaginal secretions are derived mainly from transudate from vaginal walls and to a lesser degree from endometrial and oviductal fluids, cervical mucus, exfoliated vaginal and cervical cells, and vulvar secretions. The secretions are composed mainly of water with electrolytes, microorganisms and their metabolic products, epithelial cells, and organic compounds. White blood cells are usually present only in small numbers.

The microbiology of the female genital tract is complex. Click here for information about the natural vaginal defense system. Isolates commonly found in the vaginal secretions include a variety of aerobic and anaerobic bacteria, yeast, viruses, and parasites.

Despite the large number of species present in vaginal flora, the most dominant species in the normal state, by far, is Lactobacillus. Influences on the flora, as well as on the amount and makeup of the secretions of the lower genital tract, include hormones (and therefore the phase of the menstrual cycle), contraceptive use, sexual activity, pH, and antibiotic use.

Vaginal lactic acid content provides an acidic pH of <4.5 in healthy adult women. It is produced via the metabolism of mainly lactobacilli and to a lesser degree vaginal epithelial cells. The low pH in turn favors growth of lactobacilli while inhibiting the growth of most other bacteria. This is essential in maintaining a healthy vaginal composition. When the balance is tipped, the complex of microorganisms changes, allowing the overgrowth of potentially pathogenic microorganisms that may have been part of the normal vaginal flora in much smaller numbers, such as Candida, Gardnerella vaginalis, and anaerobic bacteria in cases of bacterial vaginosis. Alternatively, sexual transmission may introduce other pathogenic organisms such as Trichomonas vaginalis, Neisseria gonorrhoeae, and Chlamydia trachomatis. These cause infection, including vaginitis, cervicitis, and pelvic inflammatory disease. Click here for the differential diagnosis of vaginal problems.