Bacterial Vaginosis (BV)

Bacterial vaginosis is easy to mistake for a yeast infection. CDC notes that women with vaginal symptoms often try over-the-counter products before or alongside a medical evaluation, and that a history alone is not enough for an accurate diagnosis and can lead to the wrong medication.^[1] BV and yeast are different conditions caused by different organisms, so an antifungal is not a BV treatment. Knowing the difference, and knowing how to confirm it, saves time, money, and prolonged symptoms.

This guide covers what BV actually is, why it develops, how it is diagnosed, the full treatment menu, and, most importantly, what to do when it keeps coming back. Every clinical claim is cited to a source, and medications and doses follow the CDC 2021 Sexually Transmitted Infections Treatment Guidelines and current FDA product labels.

What Is Bacterial Vaginosis?

Bacterial vaginosis is a state of vaginal dysbiosis, meaning the normal balance of bacteria in the vagina has shifted in a harmful direction. In a healthy vagina, Lactobacillus species usually dominate. Vaginal lactobacilli acidify their surroundings to a pH that matches the Lactobacillus-dominated vagina, which is pH 3.6 to 4.5 in most women.^[14] In BV, CDC describes replacement of the normal hydrogen peroxide and lactic acid producing lactobacilli by high concentrations of anaerobic bacteria,^[1] and vaginal pH rises above 4.5.^[14] This flora is not static: in healthy women, lactobacillus levels can change dramatically over a month.^[9]

Although the mix varies between women, species such as Gardnerella and Atopobium are among those found most frequently in BV.^[30] In one molecular study, women without BV had 1 to 6 bacterial species per sample, mostly lactobacilli, while women with BV had 9 to 17, including newly recognized species.^[8] A notable feature of BV is a polymicrobial biofilm on vaginal epithelial cells.^[1] Even among women without symptoms, a large sequencing study found one community type with fewer lactic acid bacteria and more strictly anaerobic organisms.^[7] BV is therefore not a classic infection with one known pathogen: CDC states that whether BV results from acquisition of a single sexually transmitted pathogen is unknown.^[1]

Because BV is a shift in an ecosystem rather than a fixed infection, it can come and go. CDC notes that certain women experience transient vaginal microbial changes, whereas others experience them for longer intervals.^[1] In a daily-sampling study, levels of Lactobacillus jensenii and Lactobacillus crispatus fell with the onset of menstruation, inversely to Gardnerella vaginalis, and marked increases in G. vaginalis were seen during menses.^[9] CDC also notes that BV prevalence increases during menses.^[1]

What Causes BV and Who Gets It

The precise trigger is not fully understood, but the risk factors are well mapped.^[1] A systematic review and meta-analysis of observational studies found BV associated with new or multiple male partners (relative risk 1.6) and with any female partner (relative risk 2.0), while condom use was associated with lower risk (relative risk 0.8).^[11] Among women who have sex with women, BV was associated with a higher lifetime number of female partners, and vaginal smears were concordant in 95 percent of monogamous couples, supporting sexual exchange of vaginal secretions as a possible mechanism.^[12]

In a longitudinal cohort of young, sexually active women, BV acquisition was independently associated with black race, cigarette smoking, vaginal intercourse, sex with an uncircumcised male partner, lack of vaginal hydrogen peroxide producing lactobacilli, and antibodies to herpes simplex virus type 2.^[13] In a 2001 to 2004 national survey, BV was associated with increasing douching frequency and inversely associated with current use of oral contraceptive pills; these are associations, not proof of cause.^[4] CDC adds that hormonal contraception does not increase risk for BV and might protect against it.^[1]

Biofilm is part of the picture. A review describes BV as a polymicrobial biofilm infection in which Gardnerella vaginalis is presumably the first species to adhere to the vaginal lining and then serves as the scaffolding to which other species adhere.^[28]

Population surveys also show that BV prevalence varies by race and ethnicity. In the national survey, prevalence was 51.4 percent among non-Hispanic Black women, 31.9 percent among Mexican American women, and 23.2 percent among non-Hispanic white women, and race and ethnicity remained associated with BV in the multivariate model.^[4] A sequencing study of women without symptoms found that vaginal community types and vaginal pH differed among ethnic groups.^[7] These are group patterns, not personal predictions, and they do not change the recommendation to diagnose and treat any symptomatic BV.

Symptoms of BV

The single most important fact about BV symptoms is that most women with BV do not have any. In the National Health and Nutrition Examination Survey, only about 15.7 percent of women with laboratory confirmed BV reported any vaginal symptoms, meaning roughly 84 percent were asymptomatic.^[4] When symptoms do appear, they tend to have a recognizable pattern.

The classic presentation is a thin, homogeneous discharge that smoothly coats the vaginal walls,^[1] often white or gray, with a strong fish-like odor, especially after sex.^[2] Some women also notice pain, itching, or burning in the vagina.^[2] In yeast infection, by contrast, typical symptoms include itching, soreness and abnormal discharge, and the discharge is often thick and curdy, although none of these symptoms is specific.^[1] Fever or pelvic pain call for prompt evaluation; see the red flags section below.

Because symptoms overlap among BV, yeast, and trichomoniasis, CDC advises a careful history, examination, and laboratory testing to find the cause of any vaginal symptoms.^[1] Because most women with BV have no symptoms, BV can go unrecognized without the correct test.^[4]

For a deeper look at the discharge and odor, see our dedicated guides on BV discharge and BV smell.

How BV Is Diagnosed

You cannot confirm BV from symptoms alone: CDC notes that a medical history alone is insufficient for accurate diagnosis of vaginitis.^[1] The two standard approaches are the Amsel clinical criteria and the Nugent laboratory score, and newer molecular tests have joined them.

Amsel criteria. Diagnosis requires at least 3 of these 4 findings: a thin, homogeneous discharge that smoothly coats the vaginal walls; clue cells on microscopy, which are vaginal epithelial cells studded with adherent bacteria; a vaginal fluid pH above 4.5; and a fishy odor before or after adding 10% potassium hydroxide (the whiff test).^[1][5] Compared with the Nugent score, the Amsel criteria have a sensitivity of 37 to 70 percent and a specificity of 94 to 99 percent.^[1]

Nugent score. Vaginal Gram stain is considered the reference standard laboratory method.^[1] The stain is scored from 0 to 10 as a weighted combination of lactobacilli, Gardnerella or Bacteroides morphotypes, and curved gram-variable rods.^[6] A score of 7 to 10 indicates BV, 4 to 6 is intermediate, and 0 to 3 is consistent with normal, lactobacillus-predominant flora.^[1][6]

Molecular testing. BV nucleic acid amplification tests (NAATs) detect specific bacterial nucleic acids, have high sensitivity and specificity, and can be run on clinician- or self-collected vaginal swabs. CDC says they should be used among symptomatic women only, because their accuracy is not well defined in women without symptoms.^[1] Clue cells themselves have also been re-examined: in a 2022 study of 500 samples read as positive for clue cells, true clue cells, with bacteria adhering directly to epithelial cells, were seen in only 56 percent; in the rest, epithelial cells were mechanically trapped in bacterial masses, forming pseudo clue cells.^[31]

Each method has tradeoffs. CDC notes that traditional methods, including the Amsel criteria and the Nugent score, remain useful for symptomatic BV because of their lower cost and ability to give a rapid diagnosis, while NAATs are reserved for women with symptoms.^[1] None of this changes the core point: a swab and a pH check beat guessing from symptoms.

What Has Changed in BV Care: 2021 to 2026

BV management has moved in three directions in recent years. First, single-dose treatment entered the guideline: the 2021 CDC update added alternative BV treatment options,^[1] including secnidazole 2 g oral granules taken once. CDC cites a phase 3 trial with clinical cure at days 21 to 30 of 53 percent with secnidazole versus 19 percent with placebo, and lists it as an alternative because of its higher cost and lack of long-term outcomes compared with recommended treatments.^[1] Second, recurrence has new trial evidence: a 2025 randomized trial found that also treating the male partner of women in monogamous relationships lowered 12-week recurrence to 35 percent versus 63 percent.^[23]

Third, non-antibiotic strategies are being tested. Dequalinium chloride, an antiseptic rather than an antibiotic, was noninferior to oral metronidazole in a 2024 randomized trial, with a similarly high cure rate and better tolerability.^[25] Boric acid, long used off-label, is not an FDA-approved drug; a 2021 safety review concluded that available data suggest it is safe at doses commonly prescribed by clinicians, while guidelines recommend avoiding it in pregnancy.^[27] And the long-standing warning against alcohol with metronidazole has been questioned: the 2021 CDC guideline calls abstaining unnecessary,^[1] and a later review found the evidence does not strongly support a clinically significant interaction.^[26]

None of this supplants the fundamentals: the recommended metronidazole and clindamycin regimens remain the backbone, and accurate diagnosis still comes before any prescription. But women with recurrent BV now have more trial-tested options to discuss with a clinician.

First-Line Treatment for BV

The 2021 CDC guidelines recommend treatment for women with symptoms. Established benefits in nonpregnant women are relief of vaginal symptoms and signs of infection; other potential benefits include a lower risk of acquiring several STIs, including HIV, HPV, and HSV-2. No data directly compare the efficacy of oral and topical medications.^[1] The three recommended regimens are listed in the table below.^[1][3]

An important practical point about alcohol. For years patients were told to avoid alcohol with metronidazole because of a feared disulfiram-like reaction. The 2021 CDC guideline states that refraining from alcohol use while taking metronidazole (or tinidazole) is unnecessary; the review it cites found no convincing evidence of a disulfiram-like interaction between alcohol and metronidazole.^[1] A later review in Sexually Transmitted Diseases likewise concluded that the evidence does not strongly support a clinically significant interaction between alcohol and oral metronidazole.^[26] For tinidazole, CDC makes the same statement in parentheses, but the evidence it describes concerns metronidazole.^[1] The FDA product labels have not changed: the metronidazole tablet and vaginal gel labels say to stop alcohol during and for at least three days after therapy, the tinidazole label says to avoid alcohol during treatment and for 3 days afterwards, and the secnidazole label says to avoid alcohol during therapy and for 2 days after.^{[34][35][36][37]} Ask your prescriber which advice applies to you.

Take the full course as prescribed, even if symptoms improve after a day or two. CDC advises refraining from sexual activity or using condoms consistently and correctly during treatment, and notes that douching might increase the risk for relapse and that no data support douching for treatment or symptom relief.^[1]

Because metronidazole is the most used first-line option, its specifics deserve their own page. For detailed dosing, the alcohol caution in full, and side effect management, see our metronidazole guide.

Alternative and Adjunctive Regimens

CDC also lists alternative regimens: clindamycin 300 mg orally twice daily for 7 days, clindamycin ovules 100 mg intravaginally once at bedtime for 3 days, secnidazole 2 g oral granules in a single dose, or tinidazole 2 g orally once daily for 2 days or 1 g orally once daily for 5 days.^[1][3] The tinidazole label gives the same two BV doses for nonpregnant women, taken with food.^[36] Clindamycin ovules have an oil base that might weaken latex condoms and diaphragms, so CDC advises against using such products within 72 hours after treatment, and CDC prefers intravaginal clindamycin cream for women with allergy or intolerance to metronidazole or tinidazole.^[1]

Secnidazole deserves a closer look because of its convenience. It is a 5-nitroimidazole antibiotic taken once, as granules sprinkled on applesauce, yogurt or pudding.^[24][37] An integrated analysis of the two placebo-controlled registration trials found it statistically superior to placebo on all primary and secondary efficacy outcomes.^[24] CDC lists it as an alternative rather than a recommended regimen because of its higher cost and lack of long-term outcomes compared with recommended treatments.^[1] No head-to-head trial against metronidazole was among the sources reviewed here.

An emerging non-antibiotic option is dequalinium chloride, a broad-spectrum antiseptic. A 2024 randomized trial compared dequalinium chloride vaginal tablets (10 mg once daily for 6 days) with oral metronidazole (500 mg twice daily for 7 days); clinical cure 7 to 11 days after starting was 92.8 percent with dequalinium chloride and 93.2 percent with metronidazole, meeting the noninferiority margin.^[25] Dequalinium chloride is not among the CDC 2021 BV regimens listed above, but it illustrates the search for options that reduce antibiotic use.

Choosing a Treatment: A Decision Framework

All of the regimens above work, but the best choice depends on the scenario. The table maps common situations to a reasonable default, with the understanding that a clinician will individualize based on allergies, preferences, and history.

The one choice that is rarely correct is doing nothing while symptoms persist, or self-treating with an antifungal on a guess. CDC notes that unnecessary use of over-the-counter products is common and can delay treatment of other causes of vaginitis.^[1] When in doubt, confirm the diagnosis first, then treat.

Why BV Keeps Coming Back

Recurrence is the rule rather than the exception. A cohort study that followed women for a year after oral metronidazole (400 mg twice daily for 7 days) found that 58 percent had BV return within 12 months, and 69 percent had return of abnormal vaginal flora; the authors concluded that current recommended treatment was not preventing recurrence in the majority of women.^[10]

Why does BV come back? Researchers have proposed several reasons, likely differing from woman to woman. In one study, BV-associated bacteria in women with recurrent BV fell steeply after vaginal metronidazole and later reemerged, suggesting that antibiotic resistance was not an important factor.^[9] A review attributes recurrence to possible persistence and re-emergence of BV-associated bacteria or a BV-associated biofilm after antimicrobials, and to reinfection from sexual partners.^[18] Partners are part of this: in a small urine study, cohesive Gardnerella biofilm was found in all 20 patients with BV and in their 10 partners, and the authors concluded that it involves both sexes and is sexually transmitted.^[29]

For a full breakdown of recurrence and how to stop the cycle, see how to get rid of BV.

Recurrent BV: Suppressive Therapy

For women with multiple recurrences, CDC says that twice-weekly 0.75% metronidazole gel (or a 750 mg metronidazole vaginal suppository) for more than 3 months has been reported to reduce recurrences, although the benefit does not persist once suppression stops.^[1] In the key randomized trial, women who responded to an initial 10 day course of metronidazole gel then used twice-weekly metronidazole gel or placebo for 16 weeks; recurrence during suppression was 25.5 percent versus 59.1 percent on placebo.^[19]

Suppression is a maintenance strategy, not a permanent cure. In the same trial, recurrence over the full 28 weeks, which included 12 weeks off therapy, was 51.0 percent with metronidazole versus 75 percent with placebo, and secondary vaginal yeast infection was significantly more common with metronidazole.^[19]

A related strategy adds boric acid. Because vaginal biofilm has been suggested to help BV bacteria persist, investigators added boric acid to treatment: in an uncontrolled retrospective chart review, women with recurrent BV treated with 7 days of an oral nitroimidazole followed by 21 days of intravaginal boric acid 600 mg had cure rates of 88 to 92 percent at 7 to 12 weeks, with cumulative cure of 87, 78, and 65 percent at 12, 16, and 28 weeks, and a 50 percent failure rate by 36 weeks.^[20] CDC describes this sequence (an oral nitroimidazole for 7 days, then boric acid 600 mg daily for 21 days, then twice-weekly metronidazole gel for 4 to 6 months) as an option supported by limited data.^[1] Boric acid is covered in depth in our boric acid for BV guide.

A longer combined regimen was described by Surapaneni and colleagues in an uncontrolled retrospective cohort: an oral nitroimidazole twice daily for 7 days with vaginal boric acid 600 mg daily for 30 days, then twice-weekly metronidazole gel for 5 months. Maintenance gel prevented symptomatic recurrence in 69.6 percent of compliant patients at 6 months, and vaginal yeast infection was a frequent complication.^[21] The live biotherapeutic approach is also active. A 2020 randomized trial tested Lactobacillus crispatus CTV-05 (Lactin-V), applied vaginally after vaginal metronidazole treatment, and found recurrence by week 12 in 30 percent of the Lactin-V group versus 45 percent on placebo.^[22] CDC notes that Lactin-V is not yet FDA cleared or commercially available.^[1]

The 2025 Male Partner Treatment Trial

A 2025 New England Journal of Medicine trial tested treating male partners. In this open-label randomized trial, every woman had BV and was in a monogamous relationship with a male partner, and every woman received first-line treatment. In the partner-treatment group, the male partner also took metronidazole 400 mg tablets and applied 2% clindamycin cream to the penile skin, both twice daily for 7 days. Recurrence within 12 weeks was 35 percent (24 of 69 women) with partner treatment versus 63 percent (43 of 68) with standard care.^[23] The data and safety monitoring board stopped the trial early because treatment of the woman only was inferior to treatment of both the woman and her partner. Side effects in treated men included nausea, headache, and metallic taste.^[23]

The 2021 CDC guideline predates this trial and states that routine treatment of sex partners is not recommended. It cites earlier trials, including a phase 3 trial in which a 7-day course of oral metronidazole for male partners did not reduce recurrence in their female partners.^[1] The 2025 trial differed by combining oral and topical treatment for men.^[23] When this page was checked, the CDC BV treatment page still carried the 2021 recommendation.^[3] Couples in monogamous relationships with recurrent BV can discuss this option with a clinician.

BV vs Yeast Infection: How to Tell the Difference

This is a common question, because the two conditions can look alike but are treated with different medication classes. BV is an overgrowth of anaerobic bacteria treated with antibiotics; yeast (vulvovaginal candidiasis) is a fungal infection treated with antifungals, several of which are sold over the counter.^[1] Vaginal pH is a useful bedside clue: a pH above 4.5 is common with BV or trichomoniasis, while yeast infection is associated with a normal pH below 4.5.^[1] Discharge, odor, and itching point in different directions too, as shown in the table in the symptoms section above.

The practical takeaway: a fish-like odor with thin discharge points to BV, while itching with thick, curdy discharge points to yeast.^[1][2] The two can occur together, and yeast can follow BV treatment; in the suppression trial, secondary vaginal yeast infection was more common with metronidazole gel.^[19] Diagnosing yeast is not simple either: the lack of rapid, simple, and inexpensive tests leads to both overdiagnosis and underdiagnosis of yeast infection.^[32] Get a diagnosis before treating. The full differential is in our BV vs yeast infection guide, and the yeast side belongs to the yeast infection pillar.

BV in Pregnancy

BV during pregnancy matters because it is associated with preterm birth. A meta-analysis of 20 articles with 290,397 observations found about twofold odds of preterm birth with BV (odds ratio 1.79), with a relative risk of 1.44.^[16] CDC notes that symptomatic BV has been associated with adverse pregnancy outcomes, including premature rupture of membranes, preterm birth, intra-amniotic infection, and postpartum endometritis.^[1]

CDC recommends BV treatment for all symptomatic pregnant women, states that metronidazole poses low risk during pregnancy, and says pregnant women can be treated with any of the recommended regimens or with oral clindamycin or clindamycin ovules. CDC advises avoiding tinidazole in pregnancy, and because data are insufficient for secnidazole, its use should also be avoided.^[1] CDC does not recommend routine BV screening of pregnant women without symptoms to prevent preterm birth,^[1] and the Canadian SOGC guideline notes there is no consensus on screening for or treating BV in the general pregnant population.^[17] Pregnant patients should have any suspected BV confirmed and managed with their obstetric care team, and guidelines recommend avoiding boric acid in pregnancy.^[27]

BV and Risk of HIV and Other STIs

The consequences of BV can extend beyond symptoms. A meta-analysis found BV associated with an increased risk of HIV acquisition in HIV-incidence studies (relative risk 1.6).^[15] CDC states that women with BV are at increased risk for acquiring STIs such as HIV, HPV, and HSV-2, that specific BV-associated bacteria can increase susceptibility to HIV, and that BV is associated with pelvic inflammatory disease.^[1] For these reasons CDC recommends that all women with BV be tested for HIV and other STIs.^[1] Whether to treat BV found without symptoms is a judgment a clinician should make with you; CDC recommends treatment for women with symptoms.^[1]

BV and Daily Life

BV is not dangerous in the way a high fever is, but its day to day toll is real. In interviews with 35 women with recurrent BV, most reported a moderate to severe impact, mainly on self-esteem and sex life. Women commonly said symptoms made them feel embarrassed, ashamed, or dirty and very concerned that others might notice the odor and discharge, and many regularly avoided sex.^[33]

Self-treatment can make things worse. CDC notes that women with vaginal symptoms often use over-the-counter or alternative products before or in addition to seeing a clinician, and that unnecessary use of over-the-counter products can delay treatment of other causes.^[1] Recurrence compounds the burden: in one cohort, 58 percent of women had BV return within a year.^[10] Women in the interview study often felt confused about why BV kept coming back and frustrated at their lack of control over recurrence.^[33] BV is common, and a correct diagnosis paired with a realistic recurrence plan helps.

The study authors concluded that further support and acknowledgement of these impacts are needed when managing recurrent BV.^[33] If the emotional impact of recurrent BV is affecting you, that is a legitimate reason to seek care, and it is one your clinician should take seriously rather than wave off.

Prevention

There is no sure way to prevent BV: CDC says healthcare providers and scientists do not completely understand how BV spreads or know how best to prevent it, and lists steps that may lower risk, including not douching, limiting your number of sex partners, and using condoms the right way every time you have sex.^[2] Douching was associated with BV in a national survey,^[4] and CDC says douching might increase the risk for relapse.^[1] Condom use was associated with lower BV risk in a meta-analysis of observational studies (relative risk 0.8).^[11] Oral contraceptive use was inversely associated with BV in the national survey,^[4] and CDC notes hormonal contraception might protect against BV.^[1]

One caveat about supplements: commercial oral and vaginal probiotics are not interchangeable with the specific Lactobacillus crispatus strain tested in trials, and CDC states that no studies support probiotic products as an adjunctive or replacement therapy for BV.^[1][22]

For women in a monogamous relationship with highly recurrent BV, partner treatment is a trial-supported strategy to discuss with a clinician, even though it is not in the 2021 CDC guideline.^[23][1] More broadly, treating symptomatic BV promptly matters, because BV is associated with the STI and pregnancy risks described in this guide.^[1][15][16]

What you cannot reliably prevent with supplements is covered next, but if BV does recur, the recurrences are manageable with the suppression and partner strategies described above, not with endless single courses.

What Does Not Work for BV

Several common approaches lack evidence or may do harm. Over-the-counter antifungal creams and suppositories are yeast treatments, and CDC notes that unnecessary use of over-the-counter products is common and can delay treatment of other causes of vaginitis.^[1] Douching, whether for hygiene or as a home remedy, might increase the risk for relapse, and no data support it for treatment or symptom relief.^[1]

CDC states that no studies support probiotic products as an adjunctive or replacement therapy for BV.^[1] The exception under study is the specific strain Lactobacillus crispatus CTV-05 in the Lactin-V trial, which did reduce recurrence, but that is an investigational live biotherapeutic, not a retail supplement, and it is not yet FDA cleared or commercially available.^[22][1] Garlic cloves, yogurt inserts, tea tree oil, and hydrogen peroxide douches are not part of any CDC BV regimen.^[1] If a home remedy sounds too good to be true, it usually is.

Red Flags: When to Contact a Clinician

BV itself is not an emergency, but several findings should prompt prompt evaluation rather than watchful waiting. Contact a clinician if you have fever, lower abdominal or pelvic pain, pain during sex, or abnormal bleeding, which can be signs of pelvic inflammatory disease or another infection.^[1] Likewise, any symptom during pregnancy, any discharge with blood, or symptoms that do not improve after a completed course warrant a revisit, and CDC advises returning for evaluation if symptoms recur.^[1] Finally, if treatment fails more than once, the working diagnosis may not be BV at all, and testing for trichomoniasis and other causes of vaginitis is indicated.^[1]

Frequently Asked Questions