Lactobacillus jensenii is a species of lactic acid bacteria commonly found as a dominant member of the normal vaginal microbiota. Its use to support vaginal health is justified by a body of scientific evidence. Several in vitro, clinical, and metagenomic studies have demonstrated that L. jensenii, along with other Lactobacillus species, plays a crucial role in maintaining the acidic vaginal environment (typically pH <4.5) by producing lactic acid and hydrogen peroxide. This acidic environment is inhospitable to many pathogenic bacteria and yeast, thus helping to prevent infections such as bacterial vaginosis (BV) and vulvovaginal candidiasis.

Research has shown that women with a vaginal microbiome dominated by L. jensenii (or closely related species such as L. crispatus) have a lower risk of acquiring sexually transmitted infections, including HIV and HPV. Clinical trials of probiotic supplements containing L. jensenii strains have indicated potential benefits in restoring healthy vaginal flora following antibiotic treatment or in cases of recurrent BV, though results can be variable depending on the formulation and study design.

Overall, the scientific validation for the use of L. jensenii to support vaginal health is strong, but not yet definitive at the level of large-scale, multi-center randomized controlled trials. Its consistent association with a healthy vaginal microbiota, however, provides a solid rationale for its use in probiotics targeting the vaginal body system.