In recent years, science has recognized that the microbiota — the collection of microorganisms that inhabit our bodies — is not just a “bacterial flora,” but a genuine metabolic and immune organ.

Research has shown that the different microbial ecosystems of the human body are not completely isolated compartments; instead, they communicate bidirectionally. In this context, a growing body of studies supports the existence of a functional connection between the gut and the vagina.

The vagina and the gut are interconnected ecosystems, with lactobacilli at the center of vaginal protection.

Some species of lactobacilli present in the gut can colonize or “replenish” the vaginal microbiota thanks to:

• the anatomical proximity of the perineal area,
• natural microbial migration (from the rectum to the vagina),
• the role of the mucosal immune system and intestinal metabolites.

This bidirectional communication is known as the “gut-vagina axis” and it represents the physiological basis for the use of oral probiotics to support genital health.

In a healthy vaginal microbiota, Lactobacilli form the main “defense block”:

• they produce lactic acid, maintaining the vaginal pH in an acidic range (3.5–4.5);
• they secrete bacteriocins and hydrogen peroxide with antimicrobial activity;
• they inhibit pathogens such as Gardnerella vaginalis, Candida albicans and E. coli;
• they modulate mucosal immune responses.

However, not all lactobacilli are the same: L. crispatus is often associated with a “more stable” vaginal flora profile.

In women of reproductive age, Lactobacillus is the dominant genus, able to maintain an acidic pH and protect against infections. Nevertheless, the hormonal environment — and the fluctuations it undergoes across different stages of a woman’s life — constantly shapes its composition.

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