Bacterial vaginosis, commonly called BV, is the most common vaginal infection worldwide, caused by a shift in the vaginal microbiome away from protective bacteria and toward a mix of other microbes. It often announces itself with a distinctive fishy odor and thin discharge, though a surprisingly large number of people with BV have no symptoms at all. The condition is treatable with antibiotics, but recurrence is frustratingly common, and the science behind why some people get it repeatedly while others never do is still catching up.
What Happens Inside the Vagina During BV
A healthy vaginal environment is dominated by Lactobacillus bacteria, which produce antimicrobial compounds that keep other microbes in check. BV develops when Lactobacillus populations sharply decline and are replaced by a diverse mix of anaerobic bacteria, organisms that thrive in low-oxygen environments.1PubMed Central. The Female Vaginal Microbiome in Health and Bacterial Vaginosis This isn’t a single invading germ taking over. It’s more like an ecosystem tipping out of balance, with the protective species losing ground and dozens of other species filling the gap.2PubMed Central. The Human Microbiome during Bacterial Vaginosis That distinction matters because BV is not technically an “infection” in the way a yeast infection or chlamydia is. There is no single pathogen you catch. It is a dysbiosis, a disruption in the community of bacteria that normally lives in the vagina.
One species closely linked to BV, Gardnerella vaginalis, deserves special mention because of its ability to form biofilms, sticky clusters of bacteria that coat the vaginal lining and resist antibiotic treatment. Research has shown that standard antibiotics like metronidazole and clindamycin, even at high concentrations, cannot fully eradicate these biofilms.3PubMed Central. Biofilm and pathogenic factor analysis of Gardnerella vaginalis associated with bacterial vaginosis in Northeast China Surviving bacteria within the biofilm can repopulate after treatment ends, which is a major reason BV tends to come back.
Recognizing the Symptoms
The hallmark symptom is a thin, whitish or grayish vaginal discharge accompanied by a musty or fishy odor. That smell has an identified chemical source: trimethylamine, a compound produced by the anaerobic bacteria that flourish during BV.4PubMed. Trimethylamine: the substance mainly responsible for the fishy odor often associated with bacterial vaginosis The odor tends to become more noticeable after sex or during a period, because semen and menstrual blood are alkaline, and alkaline conditions release more trimethylamine from the discharge.
BV does not typically cause the intense itching, burning, or redness associated with yeast infections or trichomoniasis. That difference is clinically useful. If vaginal irritation and a thick, clumpy white discharge are the main complaints, a yeast infection is more likely. If the discharge is profuse and yellow-green with vulvar irritation, trichomoniasis is a stronger possibility.5PubMed. Treatment of vaginal infections: candidiasis, bacterial vaginosis, and trichomoniasis BV’s signature is subtler: a persistent odor and a watery discharge without much physical discomfort.
That subtlety is part of the problem. Asymptomatic BV is common, meaning someone can have the full microbial disruption without noticing anything wrong.6PubMed Central. Asymptomatic Bacterial Vaginosis: To Treat or Not to Treat? Some people who technically have symptoms don’t recognize them as signs of an infection. Studies in pregnant populations have found a high burden of asymptomatic BV, which raises questions about screening because untreated BV during pregnancy carries real risks.7PubMed Central. Asymptomatic Bacterial Vaginosis in Pregnancy and Missed Opportunities for Treatment: A Cross-Sectional Observational Study
How You Get It
This is one of the most debated questions in the field. BV has long been classified as not sexually transmitted, and you will still find that statement on many health websites. But the picture is more complicated than that framing suggests, and researchers have been arguing about it for decades.
A substantial body of evidence ties BV to sexual activity. A recent review concluded that sexual activity is the predominant mode of initial BV acquisition and that no data directly link non-sexual factors to BV development.8PubMed Central. Bacterial vaginosis: an overlooked STI? BV is common among women who have sex with women, and concordance rates of G. vaginalis between sexual partners are high. On the other hand, G. vaginalis has been found in adolescents who have never had penetrative sex, and treating male partners with antibiotics has historically not prevented recurrence. Some researchers have proposed calling BV a “sexually enhanced disease” rather than a sexually transmitted infection, reflecting the idea that sexual activity is a critical factor without being a strict requirement.9PubMed Central. The epidemiology of bacterial vaginosis in relation to sexual behaviour
The overall evidence does not clearly support a purely endogenous origin or a purely exogenous one.10PubMed. Bacterial vaginosis. Transmission, role in genital tract infection and pregnancy outcome: an enigma What can be said is that frequency of intercourse, new sexual partners, and both penetrative and non-penetrative sexual contact all increase the odds of developing BV. Condom use is slightly protective. Douching has also been statistically associated with BV.11PubMed Central. Prevalence of Bacterial Vaginosis and Its Association with Risk Factors among Nonpregnant Women: A Hospital Based Study
Other Risk Factors
Beyond sexual behavior and douching, a few other factors seem to raise the likelihood of BV. Irregular vaginal bleeding, for instance, was a strong predictor in one longitudinal study: women who experienced irregular bleeding during the study period were more than twice as likely to develop BV. The same study found that women who already had an intermediate vaginal flora at baseline, not quite BV but not fully Lactobacillus-dominant either, were more than three times as likely to go on to develop full BV.12PubMed Central. Risk of Bacterial Vaginosis in Users of the Intrauterine Device: A Longitudinal Study IUD use is sometimes mentioned as a risk factor, but in that same study, after adjusting for other variables, IUD use itself was not significantly associated with BV. The appearance of higher risk in IUD users was explained by the fact that IUD users were more likely to have intermediate flora and irregular bleeding at baseline.
Genetics may play a role as well. Research has linked variations in genes that govern the vaginal mucosal immune response, including toll-like receptors and certain cytokine genes, to higher susceptibility to BV.13PubMed Central. Genetic predictors for bacterial vaginosis in women living with and at risk for HIV infection For example, a specific variant in the TLR4 gene was associated with a roughly 50 percent increase in the risk of BV in one study of HIV-positive adolescents.14PubMed Central. Toll-like receptor gene variants associated with bacterial vaginosis among HIV-1 infected adolescents These immune gene findings help explain why some people seem to get BV repeatedly while others with similar behaviors do not. Your innate immune system’s ability to detect and respond to shifts in vaginal bacteria varies from person to person.
Racial Disparities in the Vaginal Microbiome
BV rates differ substantially across racial groups, and this is not just a matter of behavioral differences. The baseline composition of the vaginal microbiome itself varies by ancestry. Women of European ancestry are more likely to have a Lactobacillus-dominated vaginal microbiome, while African American women are more likely to have a diverse microbial profile even in the absence of symptoms. African American women are about twice as likely to be diagnosed with BV.15PubMed Central. Differences in vaginal microbiome in African American women versus women of European ancestry
This creates a diagnostic wrinkle. The standard diagnostic tools were largely developed and validated in populations where Lactobacillus dominance is the norm, meaning they may overdiagnose BV in women whose natural vaginal flora looks “diverse” by those standards but is perfectly healthy for them. Machine learning models trained on vaginal microbiome data perform differently across racial groups, with the highest accuracy for white and Black women and lower accuracy for Hispanic and Asian women.16npj Digital Medicine. Ethnic disparity in diagnosing asymptomatic bacterial vaginosis using machine learning The takeaway for patients is that BV diagnosis is not as straightforward as it seems, and a single test result should be interpreted in context.
How BV Is Diagnosed
In clinical practice, BV is diagnosed using one of two main methods. The Amsel criteria are a bedside checklist: a clinician looks for at least three of four signs, including thin homogenous discharge, a fishy odor when the discharge is exposed to an alkaline solution, elevated vaginal pH, and the presence of “clue cells” under a microscope (vaginal cells coated in bacteria that give them a stippled appearance). The Nugent score is a lab-based method that grades a Gram-stained vaginal smear on a 0-to-10 scale based on the ratio of Lactobacillus to other bacterial types.
The Nugent score is considered the gold standard, and it has good reliability between different observers.17PubMed Central. Evaluation of interobserver reliability of Nugent score for diagnosis of bacterial vaginosis The Amsel criteria, while convenient because they can be done in the exam room, have notable limitations. In one study comparing the two methods, only about 37 percent of women with BV-positive Nugent scores met the Amsel criteria.18PubMed Central. Utility of Amsel criteria, Nugent score, and quantitative PCR for Gardnerella vaginalis, Mycoplasma hominis, and Lactobacillus spp. for diagnosis of bacterial vaginosis in human immunodeficiency virus-infected women That’s a lot of missed cases.
Newer rapid point-of-care tests are in development. One approach, the BVBlue test, detects an enzyme produced by BV-associated bacteria and has shown sensitivity around 88 percent and specificity around 95 percent compared to the Nugent score.19PubMed Central. Evaluation of a point-of-care test, BVBlue, and clinical and laboratory criteria for diagnosis of bacterial vaginosis Another prototype uses paper strips combined with smartphone microscopy to detect vaginolysin, a toxin produced by G. vaginalis, and to visualize clue cells without laboratory equipment.20PubMed Central. Rapid Point-of-Care Test Kit for Bacterial Vaginosis: Detection of Vaginolysin and Clue Cells Using Paper Strips and a Smartphone Tests like these could eventually make BV diagnosis accessible in settings without microscopes or trained lab staff.
Standard Treatment
The first-line treatments for BV are metronidazole and clindamycin. Metronidazole can be taken orally or applied as a vaginal gel; clindamycin is typically used as a vaginal cream or ovule. Trials comparing these options have found no meaningful difference in cure rates. In one head-to-head trial, about 68 percent of participants were cured with vaginal clindamycin and about 67 percent with oral metronidazole.21PubMed. Vaginal clindamycin and oral metronidazole for bacterial vaginosis: a randomized trial Another comparison of oral metronidazole, metronidazole gel, and clindamycin cream found cure rates of roughly 75 to 86 percent with no significant difference between the three.22PubMed. Treatment of bacterial vaginosis: a comparison of oral metronidazole, metronidazole vaginal gel, and clindamycin vaginal cream
The vaginal clindamycin option was noted to be better tolerated than oral metronidazole, which can cause nausea and a metallic taste and interacts poorly with alcohol. So the choice often comes down to personal preference and side-effect tolerance rather than any difference in how well the drug works. One important caveat from that second study: DNA testing showed that G. vaginalis could remain detectable even after a clinical cure, hinting at why recurrence is so common.
The Recurrence Problem
This is perhaps the most frustrating aspect of BV. An unacceptably high proportion of women experience recurrence within six months of completing standard antibiotic therapy.23PubMed Central. Bacterial vaginosis: drivers of recurrence and challenges and opportunities in partner treatment Recurrence has been attributed to several possible mechanisms: the persistence of BV-associated bacteria within biofilms that antibiotics fail to eradicate, the re-emergence of those bacteria after treatment, and reinfection from sexual partners.
One promising approach to preventing recurrence involves reintroducing protective Lactobacillus after antibiotic treatment. A randomized trial of Lactin-V, a vaginal product containing live Lactobacillus crispatus, found that BV recurred in about 30 percent of women receiving the treatment by week 12, compared to 45 percent receiving a placebo. The protective effect held through 24 weeks as well.24PubMed Central. Randomized Trial of Lactin-V to Prevent Recurrence of Bacterial Vaginosis A separate, smaller trial using a different lyophilized L. crispatus preparation similarly found about half the recurrence rate in the treatment group compared to placebo, with recurrence also taking longer to occur.25PubMed. Efficacy and safety of vaginally administered lyophilized Lactobacillus crispatus IP 174178 in the prevention of bacterial vaginosis recurrence Follow-up research on Lactin-V also showed a sustained reduction in genital inflammation, suggesting the benefit goes beyond just changing which bacteria are present.26The Lancet Microbe. Genital immune modulation by a Lactobacillus crispatus-based live biotherapeutic (LACTIN-V) following standard bacterial vaginosis treatment
Should Male Partners Be Treated Too?
For years, the standard advice was that treating male sexual partners does not help prevent BV recurrence. A landmark 2025 trial challenged that assumption: when male partners received combined oral and topical antibiotic treatment alongside the woman’s standard therapy, BV recurred in 35 percent of women within 12 weeks, compared to 63 percent when only the woman was treated. The trial was stopped early because the difference was so clear.27PubMed. Male-Partner Treatment to Prevent Recurrence of Bacterial Vaginosis
That result generated considerable excitement, but the broader picture is not yet settled. A subsequent meta-analysis pooling data from multiple trials found no overall significant benefit from male partner treatment, with the combined effect essentially neutral. When the analysis excluded the one trial that used combined oral and topical therapy for partners and looked only at trials using single-agent partner treatment, the result was flat. The meta-analysis concluded that male partner monotherapy is unlikely to reduce BV recurrence.28PubMed. The efficacy of male partner treatment to prevent recurrence of bacterial Vaginosis: A systematic review with Meta-Analysis of randomized controlled trials The takeaway is nuanced: it may matter what the male partner is treated with. Combined oral and topical therapy targeting the penile biofilm seems to work where a single oral antibiotic does not. This is an active area of research, and clinical guidelines may shift as more trials report results.
Vaginal Microbiome Transplantation
For people with BV that keeps returning despite repeated rounds of antibiotics, an experimental approach borrowed from gut medicine is showing early promise. Vaginal microbiome transplantation, or VMT, transfers vaginal fluid from a healthy donor with a Lactobacillus-dominant microbiome to a recipient whose microbiome is persistently disrupted. The first proof-of-concept study treated five women with intractable, recurrent BV, and four achieved full long-term remission lasting up to 21 months, with their vaginal microbiomes successfully converting to Lactobacillus dominance.29Nature Medicine. Vaginal microbiome transplantation in women with intractable bacterial vaginosis
More recent work has explored what pre-treatment is needed to help donor bacteria take hold. One trial found that using an antiseptic wash before transplantation led to conversion in half of recipients, while saline wash followed by VMT or antiseptic alone did not work.30The Lancet Microbe. Vaginal microbiota transplantation for treatment of vaginal dysbiosis without the use of antibiotics A recent pilot trial showed Lactobacillus dominance in 75 percent of VMT recipients at four weeks.31PubMed Central. Advances in treating bacterial vaginosis: recognizing sexual transmission and pipeline of therapies One remarkable case involved a VMT recipient whose donor-derived L. crispatus remained stable throughout a subsequent pregnancy that ended in a full-term delivery, after the patient had previously experienced multiple pregnancy losses. VMT is still in early-phase trials and not widely available, but for people who have exhausted standard options, it represents a genuinely new direction.
Why BV Matters Beyond Discomfort
Left untreated, BV raises the risk of several serious health outcomes. During pregnancy, BV is associated with roughly a 1.4 to 1.8-fold increased risk of preterm delivery and low birth weight.32PubMed. Association between bacterial vaginosis and preterm delivery of a low-birth-weight infant 33PubMed. Effect of bacterial vaginosis on preterm birth: a meta-analysis Other obstetric complications linked to BV include early miscarriage and postpartum endometritis.34JAMA. Screening for Bacterial Vaginosis in Pregnant Persons to Prevent Preterm Delivery: US Preventive Services Task Force Recommendation Statement
Outside of pregnancy, BV increases susceptibility to sexually transmitted infections, including HIV. A meta-analysis found that BV was associated with roughly 60 percent higher risk of HIV acquisition.35PubMed Central. Bacterial vaginosis and HIV acquisition: A meta-analysis of published studies The mechanisms behind this include disruption of the mucosal barrier and an increase in inflammatory signals in the genital tract.36PubMed Central. The role of bacterial vaginosis and trichomonas in HIV transmission across the female genital tract BV also raises susceptibility to other STIs and can increase the risk of pelvic inflammatory disease after gynecologic procedures.
The Emotional Toll
What often gets left out of clinical discussions is how much BV, especially recurrent BV, affects quality of life. In one survey, about three-quarters of respondents reported that BV negatively affected their mental health, and a similar proportion reported a negative impact on their sexual health. About two-thirds said it hurt their overall quality of life.37PubMed Central. Impact of (recurrent) bacterial vaginosis on quality of life and the need for accessible alternative treatments
The psychological effects can persist even after symptoms resolve. In one study, over 90 percent of women who had recovered from BV reported ongoing worry about whether people around them could detect vaginal discharge or odor, even though their symptoms had fully cleared. These intrusive thoughts affected mood, self-confidence, and social interactions throughout the day.38PubMed Central. Dependence of the dynamics of changes in the quality of life of patients with bacterial vaginosis on local levels of TNF-α and IL-1β Recurrent BV compounds these effects because each episode reinforces the anxiety cycle. Anyone dealing with this should know that the emotional weight of the condition is well documented and not an overreaction to a “minor” infection.