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Health condition · Clinically reviewed

Bacterial vaginosis, the microbiome, and getting recurrence under control.

The most common cause of abnormal vaginal discharge in women of reproductive age. Not an STI, but sex-associated - and very treatable when the diagnosis is right.

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Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against BASHH, NICE CKS and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects the 2024 BASHH BV guideline and current UK sexual-health practice.

Key facts

Bacterial vaginosis at a glance.

The essentials, in plain English - what it is, how common it is, and how it is treated in the UK today.

  • What it is

    A disruption of the vaginal microbiome - loss of protective Lactobacillus and overgrowth of anaerobes like Gardnerella, Prevotella, Atopobium and Mobiluncus.

  • How common

    The most common cause of abnormal vaginal discharge in women of reproductive age - around 3 in 10 at any given time.

  • Is it an STI

    No - but it is sex-associated. New or multiple partners, female partners and unprotected sex all raise the risk.

  • Classic symptom

    A thin, grey-white discharge with a fishy odour that is often worse after sex or during a period.

  • First-line therapy

    Oral metronidazole 400 mg twice a day for 5 to 7 days, or a 5-day course of vaginal metronidazole gel.

  • Recurrence

    Common - more than half of women have a recurrence within a year. Suppressive regimens and adjuncts can help.

Why this guide matters

The microbiome matters more than the label.

BV is common, misdiagnosed often and under-treated when it comes back. Three points shape everything else on this page.

  • It is not thrush

    Thin grey discharge with a fishy smell and little itching is BV until proven otherwise - very different from thrush and treated differently.

  • Metronidazole is first-line

    Oral or vaginal metronidazole is the BASHH first-line choice - clindamycin is a solid second-line in intolerance.

  • Recurrence needs a plan

    More than half of women have BV again within a year - suppressive regimens, adjuncts and lifestyle changes all help.

How the diagnosis is made

From first symptoms to a clear plan.

The steps a UK GP or sexual-health clinic will normally follow, in order - so you know what to expect and why.

  1. 01

    Assessing

    History and symptom review

    Discharge character, odour, timing with sex and periods, contraception, partners and any pregnancy plans.

  2. 02

    Assessing

    Speculum examination

    Looks for the classic thin, homogeneous grey-white discharge coating the vaginal walls with minimal inflammation.

  3. 03

    Assessing

    Vaginal pH

    A pH above 4.5 is one of the four Amsel criteria - a simple bedside test that supports the diagnosis.

  4. 04

    Confirming

    Amsel criteria

    Three of four - thin homogeneous discharge, pH above 4.5, positive whiff test with KOH and clue cells on wet mount - confirms BV.

  5. 05

    Confirming

    Nugent score or NAAT

    Gram-stain Nugent scoring is the microscopy gold standard. Molecular NAATs are increasingly used in UK sexual-health clinics.

  6. 06

    Preparing

    Full STI screen

    Chlamydia, gonorrhoea, trichomonas, HIV and syphilis - because symptoms overlap and co-infection is common.

  7. 07

    Preparing

    Pregnancy test if relevant

    Guides treatment choice - some regimens are avoided in pregnancy and BV in pregnancy has its own risks.

Typical timeline: from consultation to a confirmed plan in a single visit for most women.

Symptoms

What BV actually looks and smells like.

Thin grey-white discharge and a fishy odour with little itching - and the features that mean something else is going on.

  • Thin grey-white discharge

    A milky, homogeneous discharge that often coats the vaginal walls - the classic BV finding.

  • Fishy odour

    A distinctive fishy smell caused by amines - typically worse after sex or during a period.

  • Minimal irritation

    Unlike thrush or trichomonas, BV usually causes little itching or soreness - odour and discharge dominate.

  • Post-coital worsening

    Semen is alkaline and raises vaginal pH - so symptoms often flare after unprotected sex.

  • Recurrent episodes

    Symptoms that return within weeks or months of treatment - a common and frustrating pattern.

  • Cyclical pattern

    Many women notice symptoms are worse around menstruation, when vaginal pH shifts.

  • Asymptomatic BV

    About half of women who meet diagnostic criteria have no symptoms - it is often picked up incidentally.

  • Red flag - pelvic pain or fever

    Pain, fever or unwell symptoms point away from simple BV and toward PID or another cause. Get seen.

Treatment

How BV is treated in the UK.

Metronidazole first, clindamycin or tinidazole as alternatives, and a structured plan for recurrence. Lifestyle changes matter too.

  • Oral metronidazole

    400 mg twice a day for 5 to 7 days - the BASHH first-line option. Avoid alcohol during and for 48 hours after treatment.

  • Vaginal metronidazole gel

    0.75% intravaginally once daily for 5 nights - similar effectiveness to oral, often better tolerated systemically.

  • Single-dose metronidazole

    2 g orally as a one-off - convenient but less effective than the 5 to 7 day course and generally avoided in pregnancy.

  • Clindamycin cream

    2% intravaginally at night for 7 nights - a useful alternative in metronidazole intolerance. Weakens latex condoms.

  • Oral clindamycin

    300 mg twice a day for 7 days - reserved for when topical and metronidazole options are unsuitable.

  • Tinidazole

    2 g as a single dose or 1 g daily for 5 days - a nitroimidazole alternative with a longer half-life than metronidazole.

  • Lactic acid gel and probiotics

    Adjuncts such as lactic acid gel and oral or vaginal Lactobacillus preparations - evidence is limited but some women find them helpful.

  • Suppressive therapy for recurrence

    Twice-weekly vaginal metronidazole gel for 4 to 6 months - considered for women with three or more episodes in a year.

In pregnancy

Treat symptomatic BV, and consider treatment in women at high risk of preterm birth.

Oral metronidazole 400 mg twice daily for 5 to 7 days is considered safe in all trimesters. The 2 g single dose is generally avoided in pregnancy. Any decision should be made with your midwife or obstetric team.

IUD and partners

Your coil does not need to come out - and male partners are not routinely treated.

An IUD does not need removing for a first episode of BV. Male partner treatment does not reduce recurrence. Female partners with symptoms are worth reviewing at the same time.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or sexual-health clinician knows your history and can tell you which parts apply to you. If in doubt, get seen.

  • BASHH. UK national guideline on the management of bacterial vaginosis (2024).

  • NICE CKS. Bacterial vaginosis.

  • RCOG. Bacterial vaginosis in pregnancy - patient information.

  • WHO. Guidelines for the management of symptomatic sexually transmitted infections.

Red flags

When BV needs closer attention.

Most BV is straightforward. These are the situations that aren’t - and where specialist input is worth having.

  • Pregnancy with symptoms

    Symptomatic BV in pregnancy raises the risk of late miscarriage, preterm birth and premature rupture of membranes - treat rather than wait.

  • High-risk preterm history

    Women with a previous preterm birth may be offered treatment even without symptoms - discuss with your obstetric team.

  • Post-procedure infection risk

    Untreated BV before termination, hysterectomy or IUD insertion raises the risk of endometritis and wound infection.

  • Pelvic pain, fever or unwell

    Points to pelvic inflammatory disease or another cause - needs same-day assessment, not a repeat course of metronidazole.

  • Persistent symptoms after treatment

    Recheck the diagnosis - trichomonas, aerobic vaginitis or desquamative inflammatory vaginitis can all masquerade as recurrent BV.

  • HIV or immunosuppression

    BV is more common and more persistent - and untreated BV raises the risk of HIV acquisition and transmission.

  • Post-menopausal bleeding or discharge

    Change in discharge after the menopause should not be assumed to be BV without a proper examination.

  • New partner with symptoms

    A female partner with symptoms may benefit from concurrent treatment - male partners are not routinely treated.

  • Recurrent episodes

    Three or more episodes in a year deserves a structured plan - suppressive therapy, adjuncts and lifestyle review.

Complications to be aware of

Untreated BV is linked with a higher risk of HIV and other STI acquisition, pelvic inflammatory disease, endometritis after procedures, wound infection after hysterectomy, and in pregnancy with late miscarriage, preterm birth and premature rupture of membranes. That is why treating symptomatic BV - and treating it well - matters.

Living with it

A treatable condition, with a clear ladder.

Four things that make the biggest difference day to day - stop douching, drop the fragrances, think about pH after sex, and plan for recurrence rather than treat it as a personal failing.

A quiet reminder

Recurrence is common. It is not your fault.

BV comes back in more than half of women within a year. A structured plan - not shame - is the answer.

  1. 01 Wash

    Skip the douche

    Douching disrupts the vaginal microbiome and is one of the strongest modifiable risk factors for BV. Water on the outside only.

  2. 02 Products

    Drop the fragrances

    Fragranced washes, wipes and bath products can shift vaginal pH. Plain water or an emollient wash is kinder to the flora.

  3. 03 Sex

    Think about pH after sex

    Semen is alkaline and can trigger flares. Condoms, a post-sex rinse of the vulva with water, or lactic acid gel can all help.

  4. 04 Escalate

    Recurrence is a plan, not a failure

    If BV keeps coming back, ask about suppressive therapy, adjuncts like lactic acid gel and Lactobacillus preparations, and a partner review.

Frequently asked

Everything we get asked about BV.

Quick answers on diagnosis, metronidazole, partners, pregnancy and recurrence.

  • What is bacterial vaginosis?

    Bacterial vaginosis is a disturbance of the normal vaginal microbiome. Protective Lactobacillus species fall away and anaerobic bacteria such as Gardnerella vaginalis, Prevotella, Atopobium and Mobiluncus overgrow. It typically causes a thin grey-white discharge with a fishy smell.

  • Is BV a sexually transmitted infection?

    No. BV is not classified as an STI. But it is strongly sex-associated - new or multiple partners, female partners and unprotected sex all raise the risk, and it is more common in sexually active women. A full STI screen is usually offered because symptoms overlap with chlamydia, gonorrhoea and trichomonas.

  • How is BV diagnosed?

    In UK practice the Amsel criteria are used at the bedside - three of four features (thin homogeneous discharge, pH above 4.5, a positive whiff test with KOH and clue cells on wet mount) confirm BV. Gram-stain Nugent scoring is the microscopy gold standard, and NAAT-based molecular tests are now widely available in sexual-health clinics.

  • What is the first-line treatment for BV?

    BASHH recommends oral metronidazole 400 mg twice a day for 5 to 7 days, or a 5-night course of vaginal metronidazole gel. Clindamycin cream is a reasonable alternative if metronidazole is not tolerated. A 2 g single dose of metronidazole is less effective and generally avoided in pregnancy.

  • Do partners need treatment?

    Male partners are not routinely treated - the evidence does not show it reduces recurrence for the woman. Female partners with symptoms often benefit from concurrent treatment, so a partner review is worth having in same-sex relationships.

  • What if BV keeps coming back?

    Recurrence is common - more than half of women have a further episode within a year. A structured plan helps: confirm the diagnosis, treat any concurrent infection, consider suppressive vaginal metronidazole gel twice a week for 4 to 6 months, add lactic acid gel or a Lactobacillus adjunct, and review triggers like douching, fragranced products and unprotected sex.

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