Bacterial vaginosis — causes and treatment
Reviewed by the My London Pharmacy clinical team, Michelle Chuku, Pharmacist Independent Prescriber
·29 July 2026
·7 min read
Quick answer
Bacterial vaginosis (BV) is a common condition caused by a change in the natural balance of bacteria in the vagina. It often causes a thin, greyish-white discharge with a distinctive fishy odour. BV is not a sexually transmitted infection and usually responds well to a short course of antibiotics.
What is bacterial vaginosis?
Bacterial vaginosis is one of the most common causes of unusual vaginal discharge in people of reproductive age. The vagina naturally contains a mix of bacteria, dominated by protective lactobacilli that keep it slightly acidic. In BV, the number of lactobacilli falls and other bacteria increase, shifting the balance and raising the vaginal pH. These protective lactobacilli produce lactic acid and other natural substances that keep unwanted bacteria in check, so when their numbers fall, conditions become more favourable for other organisms to multiply and symptoms to appear.
BV is one of the most common vaginal conditions in people of reproductive age, and episodes can come and go over months or years. It is not a reflection of how clean someone is, and it is nothing to feel embarrassed about.
Importantly, BV is not classed as a sexually transmitted infection, and it is not caused by poor hygiene. It is very common, can come and go, and is nothing to feel embarrassed about. Understanding what it is can make it easier to recognise and treat.
Symptoms and how it is diagnosed
The most recognisable symptom of BV is a thin, greyish-white discharge with a strong, fishy smell that is often more noticeable after sex. Unlike thrush, BV does not usually cause itching or soreness, and many people have no symptoms at all.
A diagnosis is usually made from your symptoms, and sometimes by testing the pH of the vaginal fluid or taking a simple swab. Because the symptoms can overlap with thrush and some sexually transmitted infections, it is worth having an accurate assessment rather than assuming — particularly if this is the first time or if symptoms are not settling.
Clinicians recognise BV from a combination of features, including the typical thin discharge, a raised vaginal pH, the characteristic odour, and particular cells seen when a sample is examined under a microscope. You do not need to know this detail, but it explains why a brief assessment or swab can give a clearer answer than symptoms alone, especially when more than one thing could be going on at the same time.
What causes BV?
BV develops when the normal balance of vaginal bacteria is disturbed. A number of things can contribute, including sex with a new or multiple partners, douching or using scented products and washes inside the vagina, and having an intrauterine device. Menstruation and semen, which are less acidic, can also temporarily raise vaginal pH.
Because the vagina is self-cleaning, washing inside it or using perfumed products tends to do more harm than good. Using plain water externally and avoiding douching helps the protective bacteria recover and can reduce the chance of BV returning.
It is worth emphasising that BV is not caused by anything you have done wrong. Many everyday factors can tip the delicate balance, and some people are simply more prone to it than others. Smoking and frequent changes of sexual partner are among the things linked with a higher chance of BV, but plenty of people develop it without any obvious reason. Because it reflects a shift in the natural mix of bacteria rather than an outside infection you have caught, the focus is on gently restoring that balance and treating symptoms when they arise.
Treatment options
BV is usually treated with antibiotics, and treatment is recommended if you have symptoms. The most common option is Metronidazole, taken as a short course of tablets. For those who prefer a vaginal treatment, Zidoval (Metronidazole) is a vaginal gel, and Dalacin 2% Vaginal Cream contains clindamycin as an alternative.
It is important to complete the full course even if symptoms improve quickly. With metronidazole tablets you should avoid alcohol during treatment and for a short time afterwards, as the combination can cause nausea and flushing. A clinician can advise which option suits you, especially if you are pregnant, breastfeeding, or have had BV before.
A typical course of treatment lasts several days, and symptoms such as the odour and discharge often begin to settle within the first few days. A vaginal treatment can be a good choice for people who experience stomach upset with tablets, while tablets may be simpler for others; there is no single right answer, and preference matters. If symptoms have not improved by the time you finish the course, it is worth returning for review rather than starting another treatment yourself.
BV, thrush or something else?
Several conditions can cause changes in vaginal discharge, and they are easy to confuse, which is why it helps to understand the differences. BV typically causes a thin, greyish-white discharge with a fishy odour and little or no itching. Thrush, a common yeast condition, more often causes a thick, white discharge with itching and soreness, and does not usually smell. Trichomoniasis, a sexually transmitted infection, can cause a frothy discharge, soreness and an odour, and needs a different treatment again.
Because these conditions overlap but are treated in different ways, guessing can mean using the wrong remedy and delaying relief. If you have had BV before and recognise exactly the same symptoms, treatment may be straightforward. A first episode, an unusual pattern, or symptoms that do not settle are all good reasons to have an assessment, so you receive the right treatment first time rather than after several attempts.
Why treating BV matters
BV is usually more of a nuisance than a danger, but there are situations where treating it is particularly worthwhile. In pregnancy, BV is sometimes associated with complications, so symptoms are worth discussing with a clinician who can advise on suitable treatment. BV can also make the vaginal tissues a little more vulnerable, which is one reason it is sometimes treated before certain gynaecological procedures.
Having BV can also slightly raise the chance of picking up some sexually transmitted infections, so if there is any possibility of exposure, a sexual health check may be sensible alongside treatment. None of this is cause for alarm, but it explains why clinicians take BV seriously, and why a proper assessment rather than repeated self-treatment is the safest approach when symptoms keep recurring or when you are pregnant.
Preventing recurrence
BV commonly comes back, and recurrence can be frustrating. Simple measures can help lower the risk: avoid douching and perfumed soaps, bubble baths and vaginal deodorants; wash the vulva with water or a plain emollient; and avoid getting shampoo in the bath water. Using condoms may help some people, as semen can affect vaginal pH.
If BV returns frequently — for example, several times a year — it is worth speaking to a clinician, who may suggest a longer or repeated course of treatment, or a maintenance approach, and can check that nothing else is contributing.
Some people ask about probiotics or products that claim to restore vaginal bacteria. The evidence for these is mixed, so while they are unlikely to do harm, they are not a reliable way to prevent BV, and a clinician can give you a balanced view. The most dependable everyday steps remain avoiding anything perfumed or harsh around the vagina, letting the area breathe, and treating episodes promptly when they occur so they are less likely to settle into a recurring pattern.
When to seek help
You should seek advice if this is your first episode, if symptoms do not clear after treatment, or if you are pregnant, as BV in pregnancy is sometimes linked to complications and is worth reviewing with a clinician. Also seek help if you have pelvic pain, a fever, or bleeding between periods or after sex, as these are not typical of BV and need assessment.
If you are unsure whether your symptoms are BV, thrush, or something else, a proper assessment gives you the right treatment sooner. Our clinical team can review your symptoms discreetly and recommend a suitable option.
Frequently asked questions
Is bacterial vaginosis a sexually transmitted infection?
No. BV is caused by an imbalance in the vagina's natural bacteria and is not classed as an STI, though it can be more common when sexually active.
Can BV go away on its own?
Mild BV sometimes settles without treatment, but if you have symptoms, a short course of antibiotics is usually recommended to clear it and ease discomfort.
Why does my BV keep coming back?
Recurrence is common. Avoiding douching and scented products helps, and a clinician can suggest a longer or repeat course if BV returns frequently.
Can I drink alcohol while taking metronidazole?
It is best to avoid alcohol during metronidazole treatment and for a short time after, as the combination can cause nausea, flushing and headache.
Does BV affect pregnancy?
BV in pregnancy is sometimes linked with complications, so it is worth discussing symptoms with a clinician who can recommend suitable treatment.