Lactobacillus fermentum is a probiotic bacterium commonly found in the human microbiota, including the vaginal tract. Scientific studies have shown that various Lactobacillus species play a critical role in maintaining the health of the vaginal environment by outcompeting pathogenic organisms through the production of lactic acid, hydrogen peroxide, and bacteriocins, which lower the vaginal pH and inhibit the growth of potentially harmful microbes.

While L. crispatus, L. jensenii, and L. gasseri are the most dominant and well-studied Lactobacillus species in the healthy vagina, L. fermentum has also been identified in the vaginal microbiome, particularly in some populations. Clinical and laboratory research demonstrates that L. fermentum can adhere to vaginal epithelial cells, produce antimicrobial substances, and compete with urogenital pathogens such as Gardnerella vaginalis and Escherichia coli. Some randomized controlled trials and pilot studies have evaluated probiotic formulations containing L. fermentum (often in combination with other Lactobacillus strains), reporting benefits in the prevention or management of bacterial vaginosis and vulvovaginal candidiasis.

However, the strongest evidence supports L. fermentum as part of a multi-strain probiotic regimen rather than as a standalone intervention. While more research is needed to fully establish its specific mechanisms and efficacy, current scientific literature supports its use for vaginal health, justifying a relatively high evidence rating.