UTIs, Yeast Infections and Your Microbiome

Two of the most common infections women deal with, and one of the most oversold answers to them. Here's what's actually going on, and what the research does and doesn't show about probiotics.

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With that said, these two conditions are extremely common, most people would rather have fewer of them, and there's a lot of confident advice out there about probiotics. So let's go through what's actually known.

Urinary tract infections

Roughly half of all women will have at least one UTI in their lifetime, and nearly one in three will have had one requiring antibiotics by the age of 24.¹ They're far more common in women than in men — the US Office on Women's Health puts it at up to 30 times more often.²

The mechanics are unglamorous. Bacteria — most often E. coli from the gastrointestinal tract — enter through the urethra and multiply. A woman's urethra is shorter, so it's a shorter trip. Most UTIs stay in the lower urinary tract, the urethra and bladder.

Recognised risk factors include sexual activity, menopause, pregnancy, not drinking enough, wiping back to front, and a weakened immune system.³

Yeast infections

A not-so-fun fact: the CDC estimates that about 75% of women will have at least one episode of vulvovaginal candidiasis.⁴ Recurrent cases — four or more in a year — affect around 4% of women globally, rising to roughly 9% in the 25 to 34 age bracket.⁵

The culprit is Candida, a yeast that already lives in the body quite happily until something lets it overgrow. Symptoms are itching, burning, and a thick white discharge.

What tips the balance? Antibiotics are a common trigger, since they clear beneficial bacteria along with the target. High blood sugar, pregnancy, hormonal shifts and a weakened immune system all contribute, as do tight or damp clothing and harsh soaps. Yeast infections are treated with antifungals.⁶

Worth knowing: yeast infections are widely self-diagnosed and widely misdiagnosed, because the symptoms overlap with several other conditions. If it's your first one, or the treatment isn't working, get it properly looked at rather than guessing.⁷

So — can probiotics help?

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This is the part you came for, and we're going to give you the real answer rather than the flattering one. We sell probiotics. We'd still rather you heard this from us than found it out later.

For urinary tract infections: the evidence isn't there

The Cochrane review pooled nine studies and 735 people, and found no significant reduction in recurrent UTI with probiotics compared to placebo. The authors were direct about the quality of what they were working with, noting a high risk of bias across the included studies and that reported effects "may be misleading or represent overestimates."⁸

The largest single trial makes the same point. It gave 252 postmenopausal women twelve months of oral Lactobacillus or a standard preventive antibiotic. The probiotic did not meet the bar for non-inferiority — women on it averaged slightly more infections. It did have one genuine advantage: unlike the antibiotic, it didn't drive antibiotic resistance.⁹

The American Urological Association's guideline on recurrent UTI makes graded recommendations about several things — fluid intake, cranberry, and others. It makes no recommendation about probiotics at all,¹⁰ which tells you where the field has landed. A urology review of the question concludes that large clinical trials are still needed before any preventive role can be claimed.²²

For yeast infections: a modest signal, with conditions attached

Here the picture is a little brighter, and a lot more specific than the internet suggests. The Cochrane review on this question looked at ten trials — and in every one of them, probiotics were used alongside antifungal medication, not instead of it. On that basis they modestly improved short-term cure rates and reduced one-month relapse. The authors rated that evidence low to very low quality, and noted it did not translate into any long-term benefit.¹¹

And for the scenario most people actually want — taking a probiotic to head off a yeast infection after a course of antibiotics — the best trial is negative. A properly powered, placebo-controlled study of 235 women found no benefit from either oral or vaginal lactobacillus, and stopped early. The authors concluded that further research on the question was "unlikely to be fruitful."¹² The CDC's position is that there's no substantial evidence supporting probiotics for treating yeast infections.⁴

Which strains have actually been studied?

If you're going to look for anything, look for the strains that have been tested rather than the genus. The two most studied for urogenital health are Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14 (originally published as L. fermentum RC-14 — same organism, later reclassified). Taken orally, they've been shown to shift vaginal flora measurably compared with placebo.¹⁶ That line of work started with a small uncontrolled series in 2001 — ten women, no control group — which was the first report that swallowed lactobacilli could be recovered from the vagina at all.²¹ Whether that shift prevents infections is the question the trials above answer less encouragingly.

You'll also see Lactobacillus acidophilus recommended everywhere for this. In fairness to it, the evidence is thin: it rests largely on a 1992 crossover study in which 33 women were recruited and 13 completed the protocol, unblinded.¹⁷ It's also not one of the species that dominates a healthy vaginal microbiome — that's usually L. crispatus, L. iners, L. gasseri and L. jensenii. Cleveland Clinic's own guidance names L. crispatus and L. rhamnosus as the best supported.¹⁸

Strain-specific, route-specific, and mostly alongside proper treatment rather than instead of it.

One more thing worth knowing, because it comes up constantly: there is no evidence that a probiotic eases the symptoms of an infection you already have. No trial has tested it. Every study in this field counts whether infections come back, not whether burning or itching settles down while one is underway. If you have symptoms now, see the box at the top of this page.

Where Flourish fits

Flourish is a living liquid probiotic taken daily to support digestive and microbiome health. It contains eleven strains across five families, several of them from the Lactobacillus family, grown together as one culture rather than blended at the end.

That's the claim we make, and it's the one we can support. We're not claiming it prevents or treats urinary tract or yeast infections, because the evidence above doesn't let us — and a company that tells you what its product doesn't do is worth slightly more trust on the things it does.

One customer's experience

We hear from a lot of people about Flourish. This is one of the messages that has stayed with us, and we're including it because it's a real thing a real person told us — not because it's evidence of anything.

This is one individual's account of her own experience. It is not evidence that Flourish treats or resolves thrush, yeast infections or any other condition, and results like this are not what anyone should expect. Thrush in a newborn, and painful nursing, both need a doctor, midwife or lactation consultant — please don't wait on a supplement for either. The FDA has also warned about giving probiotic products to infants without medical supervision.²⁰

The unglamorous things that do help

Since we've spent this long explaining what probiotics can't be relied on to do, it's only fair to point at what your doctor will actually suggest: drink enough water, don't hold it, wipe front to back, urinate after sex, choose breathable underwear over damp or tight clothing, skip the harsh soaps and douches, and take any prescribed course of treatment all the way to the end.^2,3

Not thrilling. Considerably better supported.

Flourish is a dietary supplement made to support digestive and microbiome health. It is not a treatment for any condition. Follow the dosage on the label. Check with your doctor before starting a new supplement — particularly if you are pregnant, breastfeeding, immunocompromised, seriously ill, or considering one for a child.

Ready to try a living probiotic?

Eleven living strains. One daily shot. For digestive and microbiome support.

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A few questions we hear a lot

Will taking a probiotic stop me getting UTIs?

The best available evidence says don't count on it. The Cochrane review found no significant reduction in recurrent UTIs versus placebo, and flagged a high risk of bias in the underlying studies.⁸ The urology guideline for recurrent UTI doesn't recommend probiotics either way.¹⁰

What about yeast infections?

There's a modest short-term signal when probiotics are used alongside antifungal treatment — rated low to very low quality, with no long-term benefit.¹¹ As a replacement for treatment, or as prevention after antibiotics, the evidence doesn't support it.¹²

Does a probiotic I swallow reach the vagina?

Some strains have been detected there after oral use, and one randomised trial showed oral GR-1 and RC-14 shifted vaginal flora more than placebo.¹⁶ But when oral and vaginal delivery have been compared directly, vaginal is the route that performs.¹³

Should I take a probiotic while I'm on antibiotics?

Plenty of people do, and it's a reasonable thing to ask your prescriber about. What the evidence doesn't support is doing it specifically to prevent a yeast infection — that's the exact question the negative trial addressed.¹² Practical timing is covered in Probiotics & Medication.

Is it safe to take probiotics in pregnancy or while breastfeeding?

Ask your obstetrician or midwife. The safety data in pregnancy are limited, and this isn't a question a blog post should answer for you.¹⁹

Can I give a probiotic to my baby?

Speak to your pediatrician first. The FDA has issued a specific warning about probiotic products given to infants, following a reported infant death linked to one in a hospital setting.²⁰ This is genuinely a conversation for a clinician.

Is there anyone who shouldn't take probiotics?

People who are immunocompromised or seriously ill should check with a doctor first — there are documented cases of probiotic organisms causing bloodstream infections in those groups.¹⁹ For most healthy adults they're well tolerated.

Important information

This article is for general education and is not a substitute for professional medical advice, diagnosis, or treatment. Urinary tract infections and yeast infections require diagnosis and treatment by a qualified healthcare provider. Never delay seeking care, or stop a prescribed treatment, on the basis of anything you read here. Probiotic effects are specific to the strain, the dose, the route of administration and the outcome studied; evidence for one product does not transfer to another. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

Sources

1. Foxman, B. (2002). Epidemiology of urinary tract infections: incidence, morbidity, and economic costs. The American Journal of Medicine, 113(Suppl 1A), 5S–13S. Source
2. Office on Women's Health, US Department of Health and Human Services. Urinary tract infections. Source
3. Mayo Clinic. Urinary tract infection (UTI) — symptoms and causes, including kidney damage and sepsis as complications of untreated infection. Source
4. Centers for Disease Control and Prevention. Vulvovaginal candidiasis — STI Treatment Guidelines. Includes the 75% lifetime estimate and the statement that no substantial evidence supports using probiotics to treat VVC. Source
5. Denning, D. W., Kneale, M., Sobel, J. D., & Rautemaa-Richardson, R. (2018). Global burden of recurrent vulvovaginal candidiasis: a systematic review. The Lancet Infectious Diseases, 18(11), e339–e347. Source
6. Sobel, J. D. (2007). Vulvovaginal candidosis. The Lancet, 369(9577), 1961–1971. Source
7. Sobel, J. D. (2007), as above — notes that the absence of simple diagnostics continues to result in both overdiagnosis and underdiagnosis of vulvovaginal candidiasis. Source
8. Schwenger, E. M., Tejani, A. M., & Loewen, P. S. (2015). Probiotics for preventing urinary tract infections in adults and children. Cochrane Database of Systematic Reviews, 2015(12), CD008772 — no significant reduction versus placebo (RR 0.82, 95% CI 0.60–1.12). Source
9. Beerepoot, M. A., ter Riet, G., Nys, S., et al. (2012). Lactobacilli vs antibiotics to prevent urinary tract infections: a randomized, double-blind, noninferiority trial in postmenopausal women. Archives of Internal Medicine, 172(9), 704–712. Source
10. American Urological Association / CUA / SUFU. Recurrent uncomplicated urinary tract infections in women: guideline. Source
11. Xie, H. Y., Feng, D., Wei, D. M., et al. (2017). Probiotics for vulvovaginal candidiasis in non-pregnant women. Cochrane Database of Systematic Reviews, 11(11), CD010496 — all included trials used probiotics as adjuvant to antifungal therapy; low to very low quality evidence; no long-term benefit. Source
12. Pirotta, M., Gunn, J., Chondros, P., et al. (2004). Effect of lactobacillus in preventing post-antibiotic vulvovaginal candidiasis: a randomised controlled trial. BMJ, 329(7465), 548. Source
13. Gupta, V., Mastromarino, P., & Garg, R. (2024). Effectiveness of prophylactic oral and/or vaginal probiotic supplementation in the prevention of recurrent urinary tract infections: a randomized, double-blind, placebo-controlled trial. Clinical Infectious Diseases, 78(5), 1154–1161. Source
14. Stapleton, A. E., Au-Yeung, M., Hooton, T. M., et al. (2011). Randomized, placebo-controlled phase 2 trial of a Lactobacillus crispatus probiotic given intravaginally for prevention of recurrent urinary tract infection. Clinical Infectious Diseases, 52(10), 1212–1217. Source
15. Cohen, C. R., Wierzbicki, M. R., French, A. L., et al. (2020). Randomized trial of Lactin-V to prevent recurrence of bacterial vaginosis. New England Journal of Medicine, 382(20), 1906–1915. Source
16. Reid, G., Charbonneau, D., Erb, J., et al. (2003). Oral use of Lactobacillus rhamnosus GR-1 and L. fermentum RC-14 significantly alters vaginal flora: randomized, placebo-controlled trial in 64 healthy women. FEMS Immunology & Medical Microbiology, 35(2), 131–134. Source
17. Hilton, E., Isenberg, H. D., Alperstein, P., France, K., & Borenstein, M. T. (1992). Ingestion of yogurt containing Lactobacillus acidophilus as prophylaxis for candidal vaginitis. Annals of Internal Medicine, 116(5), 353–357 — 33 women recruited, 13 completed the protocol, unblinded. Source
18. Cleveland Clinic. Probiotics for vaginal health — names L. crispatus and L. rhamnosus among the best-supported strains. Source
19. National Institutes of Health, Office of Dietary Supplements. Probiotics — fact sheet for health professionals, including reports of bacteremia and fungemia in severely ill or immunocompromised individuals. Source
20. US Food and Drug Administration (2023). FDA raises concerns about probiotic products sold for use in hospitalized preterm infants. Source
21. Reid, G., Bruce, A. W., Fraser, N., Heinemann, C., Owen, J., & Henning, B. (2001). Oral probiotics can resolve urogenital infections. FEMS Immunology & Medical Microbiology, 30(1), 49–52 — an uncontrolled series of 10 women, and the first report that orally taken lactobacilli could be recovered from the vagina. Source
22. Akgül, T., & Karakan, T. (2018). The role of probiotics in women with recurrent urinary tract infections. Turkish Journal of Urology, 44(5), 377–383 — concludes that further large clinical trials are needed to establish any preventive or curative role for probiotics in UTIs. Source