NORMAL VULVOVAGINAL ECOSYSTEM
The vulva and vagina are covered by stratified squamous epithelium. The vulva contains hair follicles and sebaceous, sweat, and apocrine glands, whereas the epithelium of the vagina is nonkeratinized and lacks these specialized ele-ments. After puberty, with maturation of the epithelial cells that occurs with estrogen stimulation, increased lev-els of glycogen in the vaginal tissues favor the growth of lactobacilli in the genital tract. These bacteria break down glycogen to lactic acid, lowering the pH from the 6 to 8 range, which is common before puberty and after menopause, to the normal vaginal pH range of 3.5 to 4.7 in the reproductive-aged woman. In addition to lactobacilli, a wide range of other aerobic and anaerobic bacteria are normally found in the vagina at concentrations of 108 to 109 colonies per mL of vaginal fluid. Because the vagina is a potential space, not an open tube, a ratio of 5:1 anaerobic: aerobic bacteria is normal.
Discharge from the vagina is normal; therefore, not all discharges from the vagina indicate infection. This distinc-tion is important to the diagnostic process. Vaginal secre-tions arise from several sources. The majority of the liquid portion consists of mucus from the cervix. A small amount of moisture is contributed by endometrial fluid, exudates from accessory glands such as the Skene and Bartholin glands, and from vaginal transudate. Exfoliated squamous cells from the vaginal wall give the secretions a white to off-white color and provide some increase in consistency. The action of the indigenous vaginal flora also can contribute to the secretion. These components together constitute the normal vaginal secretions that provide the physiologic lu-brication that prevents drying and irritation. The amount and character of this mixture vary under the influence of many factors, including hormonal and fluid status, preg-nancy, immunosuppression, and inflammation. Asympto-matic women produce approximately 1.5 g of vaginal fluid per day. Normal vaginal secretions have no odor.