An acidic compound produced in muscular areas of the human body. The vaginal canal naturally produces some lactic acid.

Lactic acid affects the acidity (pH) of the vagina, which can in turn affect the growth of vaginal flora. Some studies suggest that lactic acid can promote growth of lactobacilli, and that healthy amount of lactic acid can reduce the risk of yeast infections. Some sexual health supplements and lubricants contain lactic acid as an active ingredient for this reason.