Contemporary perspectives on vaginal pH and lactobacilli.

Ever since the pH of the vagina was found to be much more acidic than blood and interstitial fluids, a belief going back more than a century has persisted that the vagina is protected from pathogenic organisms by the high level of hydronium ions present. A corollary of this belief is that the pH of the vagina and antipathogen activity is due to colonizing Lactobacilli. Unfortunately, this dogma lacks empirical research support. The vaginal pH is determined by the interplay between vaginal physiological processes and microbiology. An acidic vaginal pH and Lactobacilli are components of multiple defense mechanisms active in protection against infection in the lower female genital tract.