There is increasing evidence that HIV transmission can be influenced by the vaginal microbiota. In women of reproductive age, optimal vaginal microbiota associated with protection against HIV are typically dominated by beneficial Lactobacillus spp. In contrast “suboptimal” microbiota or vaginal dysbiosis is characterised by a dramatic depletion of vaginal lactobacilli and an increase in load and diversity of anaerobic bacteria. These highly diverse vaginal microbiota are prevalent in adolescent girls and young women in sub-Saharan Africa who are up to three times more likely to be infected with HIV compared to their male counterparts. Vaginal dysbiosis is associated with an increase in vaginal pH, breakdown of the protective mucosal barrier and subclinical genital inflammation, the latter resulting in the activation and recruitment of HIV target cells. In addition there is a dramatic depletion of a major microbiota organic acid metabolite, lactic acid. Here, studies will be presented demonstrating that lactic acid produced by the vaginal microbiota has microbicidal and virucidal activities that may protect against sexually transmitted infections and endogenous opportunistic bacteria as well as immune modulatory properties on the cervicovaginal epithelium that could decrease HIV susceptibility. These findings highlight the potential use of lactic acid containing agents in the lower female reproductive tract as adjuncts to female-initiated strategies to reduce HIV acquisition