The essentials

Bacterial vaginosis (BV) is the most common vaginal condition in women of childbearing age. It is not a classic infection with one germ but an imbalance: protective lactobacilli drop and other bacteria take over. It often causes a thin, grayish discharge with a fishy odor, but many women have no symptoms. A swab test confirms it, and prescription antibiotics treat it, though it often comes back.

What is bacterial vaginosis (BV), at a glance?

  • What it is: a shift in the vaginal bacteria, with fewer lactobacilli and more bacteria such as Gardnerella. The exact cause is unknown[1].
  • How common: about 23% to 29% of women of reproductive age worldwide[2][8]. It is the most common vaginal condition in women aged 15 to 44 in the United States[1].
  • Is it an STI? Not in the classic sense. It is linked to sex and rarely affects women who have never had sex, but it can also occur without sexual activity[1].
  • Key tests: vaginal pH, a look under the microscope (Amsel criteria), a Gram stain scored from 0 to 10 (Nugent score) or a molecular test (PCR)[3].
  • Not a blood test: BV is diagnosed on vaginal fluid, not on blood or urine. A full STI screening is a separate set of tests.

What are the symptoms of BV?

  • Common A thin, white or gray discharge that coats the vaginal walls[3].
  • Common A strong fish-like odor, especially after sex[1].
  • Possible Itching, irritation or burning when you urinate[2].
  • Common No symptoms at all: many women with BV do not notice anything[1]. In the study that defined the clinical criteria, more than half of the women diagnosed had no symptoms[5].

Thick, white, "cottage cheese" discharge with strong itching points more to a vaginal yeast infection (candidiasis). Yellow-green discharge, pain in the lower belly or bleeding after sex can suggest chlamydia, gonorrhea or trichomoniasis. The two can coexist, which is why a test is better than a guess.

When should I see a doctor for BV?

When to see a doctor

  • Emergency: call 911 for severe pain in the lower belly with fever, fainting, or heavy bleeding, especially if you might be pregnant.
  • Within 24 to 48 hours if you are pregnant and notice new discharge or odor: BV during pregnancy is treated when it causes symptoms[3], because untreated BV is linked to preterm birth and low birth weight[1]. Also see a clinician soon for pelvic pain, fever or a new sex partner with symptoms.
  • At your next appointment for an unusual discharge or a fishy odor without pain, or if BV keeps coming back.

What causes bacterial vaginosis, and who is at risk?

Researchers do not know exactly what triggers BV[1]. Several factors upset the balance:

  • Common Douching and vaginal washing, which increase the risk[1][2].
  • Common A new partner, several partners, or sex without condoms[1]. BV can also pass between female partners[1].
  • Possible An intrauterine device (IUD), linked to BV in the original Amsel study[5].
  • Rare No sexual activity at all: BV is uncommon in women who have never had sex[1].

BV matters beyond comfort: it increases the risk of getting HIV and other sexually transmitted infections such as chlamydia and gonorrhea[1][2].

How is BV diagnosed, and how do I read my vaginal swab results?

During a pelvic exam, the clinician takes a sample of vaginal fluid with a swab. Depending on the clinic, the result combines a bedside reading and laboratory tests. Here is a fictitious report.

Fictitious example of a vaginal swab report (United States format)
TestResultReference rangeFlag
Vaginal fluid pH5.43.8-4.5H
Clue cells (wet mount)PresentAbsentA
Amine (whiff) test, KOHPositiveNegativeA
Gram stain, Nugent score80-3H
Trichomonas vaginalis, NAATNot detectedNot detected
Candida species, NAATNot detectedNot detected
  1. pH, flagged H: a healthy vagina is between 3.8 and 4.5. Above 4.5 fits BV, but pH alone cannot diagnose it[4].
  2. Clue cells: vaginal cells covered with bacteria, seen under the microscope[3].
  3. Whiff test: a fishy odor when a drop of potassium hydroxide (KOH) is added[3].
  4. Nugent score, flagged H: 0 to 3 is normal, 4 to 6 intermediate, 7 to 10 BV[3][6].
  5. Not detected: trichomoniasis and yeast, which can cause similar symptoms, were not found.

A swab report, a urinalysis and an STI panel on the same day? BloodSense reads every line of your complete report, explains which results fit together and helps you prepare your questions for your clinician.

Get my full report explained

Amsel criteria: the bedside diagnosis

BV is diagnosed when at least 3 of these 4 signs are present: a thin, milky discharge coating the vaginal walls; clue cells under the microscope; a vaginal pH above 4.5; and a fishy odor before or after adding KOH[3][5]. Compared with the Gram stain, Amsel criteria miss 30% to 63% of cases but rarely give a false alarm (specificity 94% to 99%)[3].

Nugent score: the laboratory reference

The Gram stain is the reference laboratory method[3]. The laboratory counts three bacterial shapes on the slide (lactobacilli, Gardnerella-type rods and curved rods) and adds them into a score from 0 to 10[6]. A result of 4 to 6, "intermediate flora", is neither normal nor clear BV: your clinician reads it with your symptoms and the Amsel signs.

PCR and multiplex tests

Molecular tests (NAAT, often PCR) look for the DNA of BV-associated bacteria and lactobacilli. Some are multiplex panels that test BV, Candida and Trichomonas from one swab[3]. In a study of 1,740 women with symptoms, one such panel found 90.5% of BV cases with a specificity of 85.8%[7]. These tests should be used only in women with symptoms[3].

What does not diagnose BV

Before the swab, avoid tampons, douching, vaginal creams or medicines and vaginal sex for 24 hours, unless told otherwise[4].

Which tests are repeated after treatment for BV?

  • No routine control test: follow-up visits are unnecessary if symptoms go away[3].
  • STI and HIV tests: all women with BV should be tested for HIV and other STIs[3]. See our guides to HIV test results and STI testing.
  • If symptoms return: a new swab confirms the recurrence before another course. BV often comes back: in one Australian study, 58% of women had BV again within 12 months[9].
  • In pregnancy: routine screening of women without symptoms is not recommended to prevent preterm birth[3]. Pregnancy swabs for group B strep look for a different bacterium.

How is bacterial vaginosis treated?

No doses are given here: your clinician chooses the treatment.

  • Prescription antibiotics: metronidazole (tablets or vaginal gel) or clindamycin (vaginal cream) are recommended; secnidazole and tinidazole are alternatives[3].
  • Finish the course, and avoid sex or use condoms consistently during treatment[3].
  • Without symptoms: BV sometimes goes away on its own[1].
  • Frequent recurrences: a longer suppressive treatment can reduce recurrences, but the benefit fades when it stops[3].

What changed recently: treating the male partner. The 2021 US guideline does not recommend routine treatment of partners[3]. In 2025, a randomized trial in monogamous couples found that also treating the male partner cut recurrence within 12 weeks from 63% to 35%[10]. Ask your clinician whether this applies to you.

How can I prevent BV from coming back?

  • Do not douche or wash inside the vagina; wash the vulva with water[2].
  • Use condoms, especially with a new partner[1].
  • Note when symptoms return (after periods, after sex, after a new partner) to discuss a plan.
  • Do not self-treat repeated "yeast infections" without a test: BV and yeast need different treatments.

Questions to ask your doctor

  1. Which test confirmed my BV: pH, Amsel criteria, Nugent score or PCR?
  2. Was my Nugent score intermediate, and what does that mean for me?
  3. Should I also be tested for chlamydia, gonorrhea, trichomoniasis and HIV?
  4. Should my partner be treated too?
  5. What should I do if the odor or discharge comes back?
  6. Does BV change anything for my pregnancy or my planned procedure?

Frequently asked questions

Can BV go away on its own?

Sometimes, yes[1]. But if you have symptoms or are pregnant, see a clinician: treatment relieves symptoms and lowers the risk of complications.

Can you have BV but no STD?

Yes. BV is an imbalance of the bacteria normally present in the vagina, not a classic STI. It does make catching an STI more likely, so testing for STIs is advised[1][3].

Can men get BV?

BV is defined in the vagina, so men do not "have BV". However, partners can share BV-associated bacteria, which is why a 2025 trial tested treating male partners[10].

Is a home pH test enough?

No. A high vaginal pH fits BV but also other conditions; pH alone cannot diagnose BV[4].

  1. Centers for Disease Control and Prevention. About bacterial vaginosis (BV). December 11, 2023. cdc.gov (accessed November 6, 2026)
  2. World Health Organization. Bacterial vaginosis. Fact sheet, November 21, 2025. who.int (accessed November 6, 2026)
  3. Centers for Disease Control and Prevention. Bacterial vaginosis. Sexually Transmitted Infections Treatment Guidelines, 2021. cdc.gov (accessed November 6, 2026)
  4. MedlinePlus. Bacterial vaginosis test. Updated September 2, 2026. US National Library of Medicine. medlineplus.gov (accessed November 6, 2026)
  5. Amsel R, Totten PA, Spiegel CA, et al. Nonspecific vaginitis. Diagnostic criteria and microbial and epidemiologic associations. Am J Med. 1983;74(1):14-22. doi:10.1016/0002-9343(83)91112-9 (accessed November 6, 2026)
  6. Nugent RP, Krohn MA, Hillier SL. Reliability of diagnosing bacterial vaginosis is improved by a standardized method of gram stain interpretation. J Clin Microbiol. 1991;29(2):297-301. doi:10.1128/jcm.29.2.297-301.1991 (accessed November 6, 2026)
  7. Gaydos CA, Beqaj S, Schwebke JR, et al. Clinical validation of a test for the diagnosis of vaginitis. Obstet Gynecol. 2017;130(1):181-189. doi:10.1097/AOG.0000000000002090 (accessed November 6, 2026)
  8. Peebles K, Velloza J, Balkus JE, et al. High global burden and costs of bacterial vaginosis: a systematic review and meta-analysis. Sex Transm Dis. 2019;46(5):304-311. doi:10.1097/OLQ.0000000000000972 (accessed November 6, 2026)
  9. Bradshaw CS, Morton AN, Hocking J, et al. High recurrence rates of bacterial vaginosis over the course of 12 months after oral metronidazole therapy and factors associated with recurrence. J Infect Dis. 2006;193(11):1478-1486. doi:10.1086/503780 (accessed November 6, 2026)
  10. Vodstrcil LA, Plummer EL, Fairley CK, et al. Male-partner treatment to prevent recurrence of bacterial vaginosis. N Engl J Med. 2025;392(10):947-957. doi:10.1056/NEJMoa2405404 (accessed November 6, 2026)

This page is general information. It does not replace the advice of a clinician, who interprets your swab results with your symptoms, your history and an examination.