Bacterial vaginosis is the most common cause of unusual vaginal discharge in women of reproductive age, yet it's often confused with thrush or dismissed as "just an infection that will clear up." It's genuinely different from both thrush and an STI, and understanding that distinction matters, because the treatment — and the reason it so often returns — is specific to BV.

For many people, the confusion starts with the pharmacy shelf: thrush treatments are widely advertised and available over the counter, so it's a natural first reach when something feels "off." But treating BV with an antifungal aimed at thrush won't touch the underlying bacterial imbalance, which is why working out which one you actually have matters before you start treating it.

What bacterial vaginosis is

A healthy vagina is dominated by lactobacilli — bacteria that keep the environment mildly acidic and crowd out organisms that could cause problems. Bacterial vaginosis happens when that balance shifts: lactobacilli numbers fall, the vaginal pH rises, and a mix of other bacteria (commonly Gardnerella vaginalis alongside several others) grows in their place.

This isn't an infection you "catch" from a single source in the way you would an STI, and it isn't caused by poor hygiene. It's an imbalance, and it's extremely common — most women will experience it at least once.

Symptoms of BV

The classic picture is a thin, watery discharge that's grey or off-white in colour, with a distinctive fishy smell that's often more noticeable after sex or during a period. Unlike thrush, BV doesn't typically cause itching, soreness or pain — the discharge and smell are usually the only clues.

Around half of people with BV have no symptoms at all and only find out incidentally, for example during a routine cervical screening appointment or an unrelated sexual health check.

What causes BV and who is more likely to get it

Several everyday factors are linked with a higher chance of the vaginal bacterial balance being disrupted:

  • Vaginal douching — washing inside the vagina removes protective bacteria along with everything else.
  • Scented soaps, shower gels, bubble baths and vaginal deodorants — these disturb the natural pH.
  • New or multiple sexual partners — sexual activity is linked with BV risk, though it isn't classed as an STI.
  • Having a copper coil (IUD) — some studies link this contraceptive method with a modestly higher BV risk.
  • Smoking — associated with a higher likelihood of BV in several studies.

Using condoms, avoiding internal washing, and switching to unscented, pH-neutral products around the vulva are the practical changes most consistently linked with lower risk.

It's worth being clear about what doesn't cause BV, because a lot of unhelpful advice circulates online: it isn't caused by not washing enough, and washing more — especially internally — usually makes things worse rather than better. The vagina is self-cleaning; water alone on the outside (the vulva) is all that's needed day to day.

How BV is diagnosed

A clinician or sexual health service can usually diagnose BV from your symptoms and a quick examination, sometimes supported by testing the vaginal pH or looking at a sample under a microscope. Because BV, thrush and some STIs can look similar to each other, testing helps make sure you're treated for the right thing rather than guessing.

Home self-testing kits for vaginal pH are available, but a clinical assessment is more reliable, particularly if this is your first episode or your symptoms don't fit the typical pattern.

Treatment options in the UK

First-line treatment is a course of metronidazole tablets, usually taken twice daily for five to seven days. For people who prefer not to take tablets, or who have mild symptoms, topical alternatives work just as well for many patients:

  • Metronidazole vaginal gel (such as Zidoval), applied internally once daily at night for five nights.
  • Clindamycin vaginal cream (such as Dalacin), applied internally once daily at night for seven nights.

Whichever option is used, symptoms typically start settling within a few days, though it's important to complete the full course even if the discharge and smell clear up early — stopping early is one of the more common reasons BV comes straight back.

A key practical point: alcohol should be avoided while taking metronidazole and for 48 hours after finishing the course. Combining the two can cause an unpleasant reaction — flushing, nausea, a fast heartbeat — similar to the reaction some people have on disulfiram for alcohol dependence.

Alongside whichever treatment you're prescribed, a few simple habits help the vaginal environment recover: switch to unscented, plain soap-free washes (or water alone) around the vulva, avoid douching or vaginal "cleansing" products entirely, and consider cotton rather than synthetic underwear, which breathes better. None of these replace treatment, but they reduce the chance of the same triggers undoing it.

Why BV keeps coming back

Recurrence is the single most frustrating feature of BV for many patients. A meaningful proportion of people experience another episode within a year of successful treatment, sometimes several. There are a few reasons for this:

  • Antibiotics clear the overgrowth of unwanted bacteria, but re-establishing a healthy lactobacilli-dominant environment can take longer, leaving a window where imbalance can return.
  • Ongoing triggers — a scented product you haven't changed, a copper coil, smoking — keep disrupting the vaginal environment even after successful treatment.
  • Some bacteria linked to BV can persist in a low-level protective layer (a biofilm) on the vaginal wall, making them harder to fully clear with a single short course.

For people with frequent recurrence, a clinician may consider a longer treatment course, a maintenance regimen of low-dose vaginal gel used a few times a week for several months, or a review of contraception and lifestyle factors that could be contributing. Vaginal probiotics are sometimes used alongside treatment, though the evidence for how much they help is still developing.

Sex without a condom during or shortly after treatment is also linked with higher recurrence rates for some people, likely because semen itself is alkaline and can temporarily raise vaginal pH. Using condoms for a couple of weeks after finishing treatment, while the vaginal environment re-stabilises, is a reasonable precaution if recurrence has been a recurring problem for you.

When to see a doctor

See a GP, pharmacist or sexual health clinic if:

  • This is your first time with these symptoms, so the cause can be confirmed.
  • You're pregnant.
  • Symptoms don't improve within a week of completing treatment.
  • BV keeps recurring — three or more episodes in a year is generally considered a pattern worth investigating further.
  • You have pelvic pain, fever, or bleeding between periods or after sex, which point to something other than straightforward BV and need assessment.

These red flags matter because, left untreated, some vaginal and pelvic infections can spread upward and contribute to more serious problems such as pelvic inflammatory disease. BV itself is not dangerous for most people, but symptoms that don't fit the usual pattern are worth a proper look rather than repeat self-treatment.

A Farmeci consultation can confirm whether BV is the likely cause of your symptoms, arrange the right treatment, and help you put together a plan if it's a recurring problem for you — your clinician will always tailor this to your individual circumstances.