Bio products for intimate health

The vaginal microbiome is built unlike the gut, and that is precisely what makes it a legitimate subject for a mechanism argument. A healthy community is not diverse — it is impoverished: in most women of reproductive age a single Lactobacillus species dominates, usually L. crispatus, L. iners, L. gasseri or L. jensenii. Diversity here is a marker of dysbiosis, not of health.

Acid is the barrier

Oestrogen drives the vaginal epithelium to accumulate glycogen. Shed cells release it, host and bacterial enzymes break the polymer down to malto-oligosaccharides and glucose, and lactobacilli ferment those to lactic acid. The result is a pH around 3.5–4.5, two orders of magnitude more acidic than the colon. The acid — not the bacterium’s general “goodness” — is the barrier: it suppresses Gardnerella vaginalis, Prevotella, Atopobium and the other obligate and facultative anaerobes that characterise bacterial vaginosis.

Stereochemistry matters too. The host makes only the L-isomer of lactic acid; the D-isomer is bacterial, and its share differs sharply by species — L. crispatus produces a great deal of D-lactate, L. iners almost none. That helps explain why L. iners-dominated communities are less stable and lapse into dysbiosis more readily, even though they are nominally lactobacillary as well. Bacteriocins and competition for epithelial adhesion sites add to the acid, but their quantitative contribution is much less well established.

Where the mechanism meets engraftment

The category’s weak point is ecology, not biochemistry. A swallowed capsule asks a bacterium that has survived the stomach and colon to then relocate to the vagina; a vaginal suppository shortens that journey but does not solve the real problem, which is that a stable community resists an incoming strain exactly as it resists a pathogen. A dysbiotic community, in turn, is protected by a polymicrobial biofilm on the epithelium that a standard metronidazole course suppresses without clearing — hence recurrence in more than half of patients within a year.

This is why clinically coherent regimens are built as antibiotic first, then repopulation, rather than as a supplement on its own. The randomised LACTIN-V trial (L. crispatus strain CTV-05, published in the New England Journal of Medicine in 2020) reported reduced vaginosis recurrence when the live product was given vaginally after metronidazole — and, in the same result, that engraftment was partial and in some women did not persist after dosing stopped. That is the honest edge of the evidence: the effect is strain-specific and demonstrated for a defined product in a defined regimen, not for “probiotics” as a class.

What follows

Regulatory status widens the gap. In the United States these products are sold as dietary supplements under DSHEA 1994 rather than as drugs: efficacy need not be shown before marketing, and claims to treat vaginosis are formally prohibited. So the label almost never says what the science says. The mechanism is real and well characterised, but it travels only with a strain identifier, a dose and a route. A genus name on a box carries none of it.