What Is Intimate Flora? Vaginal Flora, pH and Lactobacilli

Intimate flora, also called vaginal flora, is the community of bacteria that lives in the vagina, and a healthy one is not "balanced" between good and bad bacteria: in most women it is dominated by a single Lactobacillus species, which turns the glycogen in vaginal cells into lactic acid and holds the pH at around 3.5.^{1, 2} In a study of 396 women, four of the five community types were each dominated by one lactobacillus species; the fifth, low in lactobacilli and rich in anaerobes, is the pattern behind bacterial vaginosis.¹ Losing that dominance, not "an imbalance of pH", is what goes wrong; the Wellgard guide to what causes BV continues the story.

Sources checked on 29 October 2026.

What is intimate flora?

Where the gut hosts hundreds of species, the vagina of a woman of reproductive age is usually run by one: Lactobacillus crispatus, L. iners, L. gasseri or L. jensenii.¹ They feed on glycogen that oestrogen lays down in the vaginal lining and release lactic acid, and the fluid they live in shifts with the cycle: see how discharge changes through the cycle. Measured without exposure to air, the pH when lactobacilli dominate is around 3.5 (range 2.8 to 4.2), and the lactic acid is concentrated enough to kill many of the bacteria associated with BV.²

What is flora in a woman?

"Flora" is the older word for the microbes living on or in a part of the body; "microbiome" means the same thing. It changes through life: sparse before puberty and after the menopause, when there is little oestrogen and glycogen, and lactobacillus-rich in between.¹

Is vaginal flora good?

Yes, when lactobacillus-dominant, and which species leads matters. Across a series of meta-analyses, women whose flora was dominated by L. iners rather than L. crispatus had 3.4 times the odds of chlamydia, while their 2.1-fold higher odds of BV (confidence interval 0.9 to 4.9) did not reach significance;³ L. iners-dominated flora is also the least stable, the pattern most often found in women who tip in and out of BV.⁸ A vaginal L. crispatus product given after antibiotics is in prescription-track trials (recurrence 30% against 45% at 12 weeks in 228 women) and is not on sale in the UK.⁴

A healthy flora is lactobacillus-dominant, not "balanced"

Health is near-monopoly: one lactobacillus species, a low pH, anaerobes kept to a trace. "My pH is off, I need to rebalance it" gets the direction wrong: the pH rises because lactobacilli have fallen. A lactic acid gel lowers it only while used; in a UK trial of 518 women with recurrent BV, symptoms had settled by two weeks in 47% on the gel against 70% on metronidazole tablets.⁵ Do I need to restore my pH if I have BV? No: when antibiotics work, lactobacilli usually return and the pH falls, though not always for good.

What happens if lactobacillus is high? Cytolytic vaginosis is an overgrowth of lactobacilli that breaks down vaginal cells and causes itching, soreness, white discharge and pain on sex or peeing, with a pH at or below 4.5 and no yeast; in one 2025 clinic series it was 19% of 103 women with vaginitis symptoms.⁶

What disturbs it, and how do I know it is off?

The triggers have been measured, and none is about cleanliness.

How do I know if my vaginal flora is off? A thin, grey-white discharge with a fishy smell, strongest after sex or a period, is the BV pattern. A thick white discharge that itches is the thrush pattern. A pH strip reading above 4.5 is one of the four clinical criteria for BV and is also raised by trichomoniasis, blood, semen or the menopause, while a normal reading with itching points away from BV and towards thrush or cytolytic vaginosis;¹⁷ what a pH strip can and cannot tell you has the detail. A "flora infection" is not a diagnosis; is it thrush, BV or something else? separates BV and thrush. How do you treat flora? You do not; the condition gets the medicine: antibiotics for BV (how is BV treated in the UK?), antifungals for thrush, and after the menopause see vaginal health after the menopause.

Can food, yoghurt or live cultures change it?

Yoghurt. Ordinary yoghurt's lactobacilli are dairy species, not the vaginal ones; yoghurt on a tampon puts sugar and foreign bacteria where they do not belong.

Live cultures by mouth. The trials are strain-specific and mostly report flora rather than symptoms. In a 544-woman oral trial, women with BV or other vaginal infections took a two-strain capsule for six weeks without antibiotics; normal flora was found in 61.5% against 26.9% on placebo at six weeks and 51.1% against 20.8% at twelve.¹³ Taken after a course of antibiotics, across ten trials of 1,234 women, live cultures were associated with BV recurrence of 14.8% against 25.5%.¹⁴ In 304 pregnant women in four UK units, a daily two-strain capsule did not change the flora or BV rates.¹⁵ A 2026 network meta-analysis found both vaginal (relative risk 0.37, moderate certainty) and oral (relative risk 0.45, low certainty) live cultures associated with fewer early recurrences after antibiotics; the grades reflect the trials behind each route, not a head-to-head test; neither replaces antibiotics.¹⁶ Anyone immunocompromised, seriously ill or with a central line should ask a pharmacist or GP first; what changes in discharge to expect and who should take care cover side effects.

What we don't know

Why one woman's flora settles on L. crispatus and another's on L. iners is unexplained; no product on sale has been shown to install L. crispatus.⁴ The trigger figures are observational: association, not proof of cause.^{7, 9, 11}

Frequently asked questions

Does eating yoghurt help with BV?

Only small trials have tested yoghurt with added lactobacilli for BV; see can I get rid of BV by taking probiotics.

How do I get Lactobacillus crispatus?

You cannot buy or eat it into place. It is favoured by oestrogen and lost to the triggers in the table; a vaginal L. crispatus product remains in prescription-track trials.⁴

What are the benefits of a healthy intimate flora?

When lactobacilli dominate, the lactic acid they make holds the pH at around 3.5 and is concentrated enough to kill many of the bacteria associated with BV.² Women whose flora is led by L. crispatus rather than L. iners have about a third of the odds of chlamydia, with BV odds leaning the same way without reaching significance.³ The NHS says BV increases the risk of getting an STI.¹²

What does it mean to have high Lactobacillus crispatus?

The most protective pattern: significantly lower odds of chlamydia than L. iners dominance, and BV odds that lean the same way.³

Oral capsules or vaginal pessaries: which is better for flora?

No head-to-head trial. The 2026 network analysis found both vaginal (relative risk 0.37) and oral (relative risk 0.45) live cultures associated with fewer early recurrences after antibiotics; neither replaces antibiotics.¹⁶

Sources

1. Ravel J, et al. Vaginal microbiome of reproductive-age women. Proceedings of the National Academy of Sciences, 2011. Cross-sectional, 396 women. PubMed 20534435.
2. O'Hanlon DE, et al. Vaginal pH and microbicidal lactic acid when lactobacilli dominate the microbiota. PLoS One, 2013. Observational, 56 women; two authors at a vaginal-products company. PubMed 24223212.
3. Carter KA, et al. Epidemiologic evidence on the role of Lactobacillus iners in sexually transmitted infections and bacterial vaginosis: a series of systematic reviews and meta-analyses. Sexually Transmitted Diseases, 2023. Meta-analyses; one author at a culture manufacturer. PubMed 36729966.
4. Cohen CR, et al. Randomized trial of a vaginal Lactobacillus crispatus live biotherapeutic and recurrence of bacterial vaginosis. New England Journal of Medicine, 2020. Randomised trial, 228 women; publicly funded. PubMed 32402161.
5. Ross JDC, et al. Intravaginal lactic acid gel versus oral metronidazole for women with recurrent bacterial vaginosis: the VITA randomised controlled trial. BMC Women's Health, 2023. Randomised open-label trial, 518 women, UK. PubMed 37161454.
6. Komec S, Aydin MD. A little-known vaginitis-like picture: cytolytic vaginosis. Clinical Laboratory, 2025. Clinic series, 140 women. PubMed 39808145.
7. Brotman RM, et al. A longitudinal study of vaginal douching and bacterial vaginosis: a marginal structural modeling analysis. American Journal of Epidemiology, 2008. Cohort, 3,620 women, one year. PubMed 18503038.
8. Tamarelle J, et al. Factors associated with incidence and spontaneous clearance of molecular-bacterial vaginosis. Sexually Transmitted Diseases, 2022. Cohort, 100 women, 10 weeks. PubMed 35969846.
9. Fethers KA, et al. Sexual risk factors and bacterial vaginosis: a systematic review and meta-analysis. Clinical Infectious Diseases, 2008. Meta-analysis, 43 studies. PubMed 18947329.
10. Vodstrcil LA, et al. Hormonal contraception is associated with a reduced risk of bacterial vaginosis: a systematic review and meta-analysis. PLoS One, 2013. Meta-analysis, 55 studies. PubMed 24023807.
11. Peebles K, et al. Elevated risk of bacterial vaginosis among users of the copper intrauterine device: a prospective longitudinal cohort study. Clinical Infectious Diseases, 2021. Cohort, 2,585 women. PubMed 32505132.
12. NHS. Bacterial vaginosis, reviewed 19 June 2026. nhs.uk/conditions/bacterial-vaginosis.
13. Vujic G, et al. Efficacy of orally applied probiotic capsules for bacterial vaginosis and other vaginal infections: a double-blind, randomized, placebo-controlled study. European Journal of Obstetrics, Gynecology and Reproductive Biology, 2013. Randomised trial, 544 women. PubMed 23395559.
14. Chieng WK, et al. Probiotics, a promising therapy to reduce the recurrence of bacterial vaginosis in women? A systematic review and meta-analysis. Frontiers in Nutrition, 2022. Meta-analysis, 10 randomised trials, 1,234 women. PubMed 36204368.
15. Husain S, et al. Effects of oral probiotic supplements on vaginal microbiota during pregnancy: a randomised, double-blind, placebo-controlled trial with microbiome analysis. BJOG, 2020. Randomised trial, 304 women, UK. PubMed 30932317.
16. Gardella B, et al. Rethinking prevention of recurrent bacterial vaginosis: a comparative effectiveness network meta-analysis. Journal of Lower Genital Tract Disease, 2026. Network meta-analysis of randomised trials. PubMed 42611724.
17. Amsel R, et al. Nonspecific vaginitis: diagnostic criteria and microbial and epidemiologic associations. American Journal of Medicine, 1983. Diagnostic study, 397 women. PubMed 6600371.

Spotted something out of date? Email support@wellgard.co.uk with the page address and the sentence.

This article is general information, not medical advice. See a GP or sexual health clinic for a first episode of unusual discharge, for any discharge in pregnancy, and whenever a pharmacy treatment has not worked; live cultures are a food supplement, not a treatment.