Bacterial Vaginosis (BV)

Symptoms, causes, diagnosis and treatment — and where to go next for detail on each.

What Is Bacterial Vaginosis?

Bacterial vaginosis is a condition caused by an overgrowth of certain bacteria in the vagina. A healthy vaginal microbiome is dominated by protective Lactobacillus species, which produce lactic acid and maintain an acidic pH of around 3.8 to 4.5. That acidity keeps other organisms in check.

In BV that balance is disrupted. Lactobacilli decrease, and anaerobic bacteria — particularly Gardnerella vaginalis, along with Prevotella and Mobiluncus species — overgrow. Vaginal pH rises above 4.5, and the anaerobes produce volatile amines, which are responsible for the characteristic fishy odour.

BV is not an infection in the conventional sense of something caught from another person, not a sexually transmitted infection, and not caused by poor hygiene. It is a shift in a microbial community, and it can develop in any woman of reproductive age — including those who have never been sexually active.

Symptoms

Around half of women with BV have no symptoms. When symptoms do occur, the pattern is distinctive: thin, watery, grey or off-white discharge with a fishy odour that is often stronger after sex and around a period. Significant itching, soreness, redness or pain are not typical of BV and suggest a different or additional diagnosis.

Causes and Risk Factors

The precise mechanism that triggers the shift in the vaginal microbiome is not fully understood. Several factors consistently increase risk, and some women develop BV with none of them present.

There is also a biological component that has nothing to do with behaviour. Vaginal bacterial communities differ between women, and some types are considerably more stable than others — which is part of why certain women recur repeatedly while others never have a second episode. That is explained in our guide to recurrent BV.

Diagnosis

BV is diagnosed clinically or through laboratory testing. The standard framework is the Amsel criteria, which confirms BV when at least three of four features are present:

• Thin, homogeneous, white-grey vaginal discharge
• Vaginal pH greater than 4.5
• A positive amine or "whiff" test — fishy odour on adding potassium hydroxide
• Clue cells on microscopy — vaginal cells coated in bacteria

In primary care and online consultation, diagnosis is usually made on reported symptoms, discharge characteristics and clinical history. A short online consultation with one of our GPhC-registered pharmacist independent prescribers can assess your symptoms and, where appropriate, issue a prescription without a GP appointment.

What a home pH swab can establish, what clinic microscopy and Hay-Ison scoring add, and the questions neither can answer are covered in our guide to BV testing at home and in clinic.

Treatment Options

BV is treated with antibiotics, all of which are prescription-only in the UK. NICE and BASHH recommend a stepped approach, with the choice depending on your preference, pregnancy status and any previous treatments.

Metronidazole tablets

The NICE first-line choice, and the treatment most women are given. If you want the background on the drug itself, what metronidazole is and what it treats explains how it targets anaerobic bacteria and why it does nothing for thrush. For practical dosing — taking it with food, spacing doses, missed doses and the alcohol rule in full — see how to take metronidazole. The complete tolerability picture, including the warfarin and lithium interactions and what warrants stopping, is in metronidazole side effects and warnings.

Zidoval vaginal gel

The same antibiotic delivered locally, over the shortest standard course at five nights. Because very little is absorbed, the nausea and metallic taste that make the tablets unpopular are far less of a problem. Application technique, the considerations table and its second role as twice-weekly suppressive therapy are covered in using Zidoval vaginal gel for BV.

Dalacin 2% cream

Clindamycin rather than metronidazole, which makes it the option when metronidazole is unsuitable or when avoiding alcohol for a week is impractical. The step-by-step method, the latex warning and the bowel-condition caution are set out in how to use Dalacin 2% cream for BV.

Other options you may have read about

Over-the-counter products such as lactic acid gels are not equivalent to prescription treatment. What the evidence supports — and what it does not, including boric acid, probiotics and common home remedies — is assessed in BV gels compared: prescription versus over-the-counter. A further nitroimidazole, tinidazole, appears frequently in US guidance and occasionally in UK prescribing; how tinidazole compares with metronidazole covers its dosing and its longer alcohol window. For what to expect once any course begins, how long BV takes to clear up sets out the timeline day by day.

BV in Pregnancy

BV in pregnancy has been associated with an increased risk of preterm birth, premature rupture of membranes, late miscarriage, low birth weight and infection of the womb lining after delivery. Those are associations found across populations rather than predictions about any individual pregnancy, and most women with BV in pregnancy deliver at term.

Symptomatic BV in pregnancy is generally treated, usually with a standard metronidazole course. High-dose regimens such as the single 2g dose are avoided. Routine screening of women without symptoms is not recommended, because treating asymptomatic BV in low-risk pregnancies has not been shown to improve outcomes.

Recurrent BV

Between 50 and 70% of women experience a recurrence within a year of successful treatment. This is the norm rather than a sign that treatment failed — antibiotics clear the overgrowth but do not rebuild the protective lactobacilli, and a bacterial biofilm on the vaginal wall can survive a standard course.

Recurrent BV, defined as three or more confirmed episodes in twelve months, has a different management pathway: extended metronidazole courses, suppressive twice-weekly vaginal gel for three to six months, systematic trigger management and, where needed, specialist referral.

BV, Sex and Partners

BV is not classed as a sexually transmitted infection, and women who have never had sex can develop it. Sexual activity does influence it, though: new partners, multiple partners and unprotected sex are all associated with higher rates, and consistent condom use is associated with fewer episodes.

UK guidance does not currently recommend routine treatment of male partners. That position is under active reconsideration following a randomised trial published in the New England Journal of Medicine in March 2025, which found substantially lower recurrence when male partners were treated concurrently. It is reasonable to raise with a clinician if you have recurrent episodes, but it is not yet routine UK practice.

Prevention

BV cannot always be prevented, but these measures reduce risk and may help prevent recurrence.

• Avoid vaginal douching or washing inside the vagina entirely
• Use unperfumed soap externally only, and avoid scented feminine hygiene products
• Stop smoking
• Consider consistent condom use, particularly with new partners
• Wear breathable cotton underwear
• Shower rather than bathe where practical, and avoid bubble bath

When to Seek Help

See a clinician if:

• You have unusual vaginal discharge, odour or discomfort
• Symptoms do not improve within three days of starting treatment
• Symptoms persist after completing a full course
• BV keeps recurring — three or more episodes in a year
• You are pregnant
• You have a recent new sexual partner and are concerned about sexually transmitted infections

BV & Treatment Guides

In-depth guides on BV, the medicines used to treat it, and the questions that come up most often.

Completing the treatment

Access Doctor supplies prescription BV treatment following an online consultation with a pharmacist independent prescriber, with discreet delivery in plain packaging.