Bacterial vaginosis (BV): symptoms, testing and why it comes back

You have noticed a thin discharge and a smell that was not there before, stronger after sex or around your period. You have washed more carefully, and it has made no difference.

The most likely cause is bacterial vaginosis, the most common vaginal infection in women of reproductive age. It is not caused by poor hygiene, it is not dangerous in most cases, and it is easily treated. It can be uncomfortable and confusing, though, particularly when it keeps coming back.

If you would like an answer today, a private GP consultation at our Harley Street clinic is £150, seven days a week. The doctor can examine you, take a swab for a BV test (£105) and prescribe treatment if you need it.

What causes bacterial vaginosis?

The vagina naturally contains a mix of bacteria. In a healthy balance, lactobacilli keep the vagina slightly acidic and hold other bacteria in check. BV happens when that balance tips and bacteria such as Gardnerella overgrow.

According to the NHS, you are more likely to get BV if you are sexually active, have a new partner or have an IUD (the copper coil). Women who have never had sex can get it too. Douching, vaginal washes and scented products make it more likely, because they strip away the protective bacteria. Washing more often tends to make BV worse, not better.

BV is not classed as a sexually transmitted infection, and you cannot catch it from swimming pools, toilet seats or shared bedding. Sex does play a part, though. It is more common after a new partner, and the 2025 partner trial described below suggests the bacteria can pass back and forth between partners.

BV symptoms, and how they differ from thrush

The typical signs are a thin, watery grey or white discharge and a fishy smell that is often stronger after sex or during a period. Some women notice mild irritation, but BV does not usually cause much itching or soreness. Half of women with BV have no symptoms.

BV is not usually painful. Pelvic pain, a fever, bleeding after sex or pain during sex point to something else, such as an STI or pelvic inflammatory disease, and are a reason to see a doctor promptly.

BV, thrush and trichomonas compared

That pH line is the useful part for a home check. Pharmacy pH kits measure vaginal acidity, and a reading above 4.5 fits BV (or trichomonas), while a normal reading with itching points more towards thrush. A kit cannot tell BV and trichomonas apart, so a test is worth having if the result is high, if this is the first time, or if thrush treatment from the pharmacy has not worked.

How is BV tested?

BV is diagnosed from a vaginal swab, not a blood test. The doctor looks at the discharge and its pH, and the swab confirms the imbalance in the lab. At our clinic the BV test costs £105.

BV and STIs such as chlamydia can cause similar changes in discharge. If there is any chance of an STI, for example after a new partner, our sexual health screening packages check several infections in one visit. They run from £250 for Bronze (consultation, examination, chlamydia, gonorrhoea, syphilis and HIV) to £665 for the Platinum female package. If you have already tested negative and the symptoms persist, our guide to symptoms with a negative test explains what to check next.

BV treatment

BV is treated with antibiotics, either tablets or a vaginal gel or cream. The UK national guideline from BASHH recommends:

• metronidazole tablets, 400 mg twice a day for 5 to 7 days, or a single 2 g dose;
• metronidazole 0.75% vaginal gel once a day for 5 days; or
• clindamycin 2% vaginal cream once a day for 7 days.

Each clears BV in about 70 to 80% of women at 4 weeks. Finish the whole course even if symptoms settle early. With metronidazole, the BNF advises no alcohol during the course and for 48 hours afterwards. Clindamycin cream can weaken latex condoms, so plan contraception around it.

If you are pregnant and your discharge changes, see a doctor or your midwife. The NHS notes a small chance of complications such as premature birth or miscarriage, although BV causes no problems in most pregnancies, and the doctor chooses a treatment suitable for pregnancy.

Left untreated, BV is linked to a higher risk of catching STIs, including HIV, and to pelvic inflammatory disease.

Why does BV keep coming back?

BV has a frustrating tendency to recur, and around half of women treated will have another episode within 12 months. The vaginal pH can stay disrupted after treatment, scented products and douching can tip the balance again, and sex with the same partner can bring the bacteria back.

That last point changed in 2025. A trial published in the New England Journal of Medicine treated the male partners of women with BV, in monogamous couples, with metronidazole tablets and clindamycin cream applied to the penis for 7 days. Within 12 weeks, BV came back in 35% of women whose partner was treated, against 63% of women whose partner was not. The trial was stopped early because the difference was so clear.

It is one trial, so talk it through with the doctor rather than treating a partner on your own. If you have had three or more episodes in a year, a longer plan can help, such as metronidazole gel twice a week for 4 to 6 months, alongside a look at what keeps restarting it.

Seeing a doctor about BV at 117a Harley Street

Book a GP if you have unusual discharge that has not cleared, a new smell, symptoms that persisted after a pharmacy thrush treatment, a new partner, or if you are pregnant or trying to conceive. Appointments run seven days a week, booked or as a walk-in when there is capacity.

For BV that keeps returning, our consultant gynaecologist Dr Hikmat Naoum offers a gynaecology consultation for £250. If you are unsure whether a GP or a gynaecologist is the better first appointment, our guide on who to see first walks through it.