What is the pH of vagina in a woman who is in reproductive age group?

Typically, the vaginal pH ranges between 4 and 4.5. It results from Lactobacillus species' production of lactic acid, fatty acids, and other organic acids. Other bacteria can also contribute organic acids from protein catabolism, and anaerobic bacteria contribute by amino acid fermentation. Stimulated by estrogens, the epithelial cells synthesize and accumulate glycogen. When the cells desquamate, bacteria metabolize glycogen to lactic acid, causing a relatively low pH within the vagina which helps provide protection against pathogenic microorganisms. Ref: Hoffman B.L., Schorge J.O., Schaffer J.I., Halvorson L.M., Bradshaw K.D., Cunningham F.G., Calver L.E. (2012). Chapter 3. Gynecologic Infection. In B.L. Hoffman, J.O. Schorge, J.I. Schaffer, L.M. Halvorson, K.D. Bradshaw, F.G. Cunningham, L.E. Calver (Eds), Williams Gynecology, 2e.