Host, microbial, and environmental drivers of vaginal microbiota composition.

The human vagina harbors a microbial community that differs markedly in compositional structure from all mammals, including closely related primates. Lactobacilli are the most abundant vaginal species, and their dominance in this niche is associated with protection against adverse health outcomes, including preterm birth, sexually transmitted infections, and bacterial vaginosis. However, the vaginal environment can also support compositions of diverse anaerobic bacteria, which have been linked to poor reproductive health outcomes. Here, we review current knowledge on host and microbial determinants that influence microbial community structure within the vaginal niche, emphasizing the interplay between host physiology, immune, and metabolic interactions, as well as lifestyle factors. This integrated understanding provides a foundation for linking vaginal microbiome compositions to clinically relevant phenotypes and highlights mechanisms that could be exploited to promote improved reproductive health.