About bacterial vaginosis

Bacterial vaginosis (BV) is a common yet poorly understood condition, in which the balance of bacteria inside the vagina becomes disrupted.

BV doesn't usually cause any vaginal soreness or itching, but often causes unusual vaginal discharge. If you have the condition, your discharge may:

  • develop a strong fishy smell, particularly after sexual intercourse
  • become white or grey
  • become thin and watery

BV isn't serious for the vast majority of women, although it may be a concern if symptoms of BV develop in pregnancy and you have a history of pregnancy-related complications.

Around half of women with bacterial vaginosis have no symptoms.

When to seek medical advice

See your GP or visit a sexual health or genitourinary medicine (GUM) clinic if you notice any abnormal discharge from your vagina, especially if you're pregnant. It's important to get this checked to rule out other infections and prevent complications.

Your doctor will ask about your symptoms and may examine your vagina. In some cases, a small sample of the vaginal discharge will be taken using a plastic loop or swab, so it can be examined for signs of BV.

Read more about diagnosing bacterial vaginosis

Why it happens

The vagina naturally contains a mix of many different bacteria. In cases of BV, the number of certain bacteria increases, affecting the balance of chemicals in the vagina.

What leads to these changes in the levels of bacteria is not clear. BV isn't classified as a sexually transmitted infection (STI), but you're at a higher risk of developing the condition if you're sexually active.

Women with BV may be able to pass the condition to other women they have sex with, although it's not clear how this happens.

There's no evidence to suggest the bacteria causing BV can affect male sexual partners.

There are also a number of other factors that can increase your risk of developing BV, including:

BV is more common in women who use a coil for contraception and those who perform vaginal douching (cleaning out the vagina).

Read more about the causes of bacterial vaginosis


BV can usually be successfully treated using a short course of antibiotic tablets or an antibiotic gel you apply inside your vagina.

In most cases, you'll be prescribed antibiotic tablets to take twice a day for five to seven days.

However, it's common for BV to return. More than half of women successfully treated with BV find their symptoms return, usually within three months. Women who have frequent episodes of BV may be referred to a GUM specialist.

Read more about treating bacterial vaginosis


If BV develops in pregnancy, it may increase the risk of pregnancy-related complications, such as premature birth or miscarriage. However, this risk is small and appears more significant for women who have had these complications in a previous pregnancy. BV causes no problems in the vast majority of pregnancies.

As a precaution, you should contact your GP or GUM clinic if you're pregnant and you begin to have vaginal discharge (although discharge can be a normal part of pregnancy).

Bacterial vaginosis can also increase your risk of getting some STIs.

Read more about the complications of bacterial vaginosis


The causes of BV aren't fully understood, so it's not possible to completely prevent it. However, you may be able to lower your risk of developing the condition if you avoid:

  • using scented soaps, perfumed bubble bath and antiseptic bath liquids
  • using vaginal deodorant
  • vaginal douching
  • using strong detergents to wash your underwear

These can upset the natural bacterial balance in your vagina, making it more likely that you'll develop BV.

Causes of bacterial vaginosis

Bacterial vaginosis (BV) occurs when there's a change in the natural balance of bacteria in your vagina.

Your vagina should contain bacteria called lactobacilli, which produce lactic acid. This makes the vagina slightly acidic, which prevents other bacteria from growing there.

Women with BV tend to have a temporary shortage of lactobacilli, which means their vagina isn't as acidic as it should be. This allows other types of bacteria to grow.

It's still unclear what causes this change, although your risk is increased if you:

  • are sexually active, particularly if you have a new sexual partner or multiple sexual partners
  • use an intrauterine device (IUD) – a contraceptive device that fits inside the womb
  • smoke

For reasons that are unclear, BV is more common in black women than in other ethnic groups.

Is BV an STI?

BV isn't generally considered a sexually transmitted infection (STI). However, there's conflicting evidence on the subject.

Evidence that suggests BV may be an STI includes:

  • rates of BV are higher in women who have multiple sexual partners
  • rates of BV are lower in women who use a condom during sex

There's also evidence that women with BV can pass the condition to women they have sex with, although how this happens is still unclear.

However, there's also evidence to suggest BV may not be an STI, as:

  • there's no equivalent of BV in men
  • treating male partners with antibiotics doesn't prevent the recurrence of BV
  • rates of BV can vary significantly in different ethnic groups, which can't be explained by sexual activity alone
  • BV can sometimes occur in women who aren't sexually active

Many experts think sexual activity plays a role in BV, but other factors are probably also responsible for the condition.

Diagnosing bacterial vaginosis

See your GP or visit a sexual health or genitourinary medicine (GUM) clinic as soon as possible if you have any abnormal discharge from your vagina.

It's important to determine whether you have bacterial vaginosis (BV) or a similar condition, such as trichomoniasis or gonorrhoea. These can both also cause abnormal vaginal discharge.

Tests for BV are sometimes offered to women during pregnancy or before certain procedures.


Your GP or healthcare professional may diagnose BV from a description of your symptoms and by examining your vagina. In particular, they'll look for:

  • a thin, greyish discharge
  • an unpleasant smell

In some cases, this may be enough to confirm your diagnosis. However, you may need further tests if you're sexually active and may have a sexually transmitted infection (STI) instead.


A sample of cells may be taken from the wall of your vagina using a plastic loop or swab. A swab looks a bit like a cotton bud, but is smaller, soft and rounded.

The swab or loop picks up samples of discharge and cells. It only takes a few seconds and isn't usually painful, although it may be slightly uncomfortable for a moment.

The samples are examined to check for signs of BV. In some centres, the result may be available immediately, but it can take up to a week to get the results if the sample is sent to a laboratory.

The level of acidity (pH) of your vagina may also be measured. A swab will be taken from inside your vagina and wiped over a piece of specially treated paper. The paper changes colour depending on the pH level. A pH level higher than 4.5 is an indication that you may have BV.

Treating bacterial vaginosis

Bacterial vaginosis (BV) can be treated successfully with antibiotics.

There's currently no evidence that probiotics, such as those found in some yoghurts, are able to treat or prevent BV.


Metronidazole is the most common and preferred antibiotic treatment for BV. It's available in three forms. These are:

  • tablets to be taken twice a day for five to seven days
  • a single larger-dose tablet you take only once
  • a gel you apply to your vagina once a day for five days

In most cases, metronidazole tablets taken over five to seven days are recommended, as they're considered to be the most effective treatment. These can be taken if you have symptoms of BV while you're pregnant.

If you're breastfeeding, metronidazole gel is usually recommended, as the tablets can affect your breast milk.

Occasionally, an alternative antibiotic may be recommended instead of metronidazole, such as clindamycin cream applied to the inside of the vagina once a day for seven days. This cream may be prescribed if you've had a reaction to metronidazole in the past, for example.

Whichever course of antibiotics you're prescribed, it's important to finish it, even if you start to feel better. This helps to reduce the risk of symptoms persisting or recurring.

Side effects 

Metronidazole can cause nausea, vomiting and a slight metallic taste in your mouth. It's best to take it after eating food. Contact your doctor if you start vomiting when you take the drug. They may recommend trying an alternative form of treatment.

Don't drink alcohol while taking metronidazole and for at least 48 hours after finishing the course of antibiotics. Drinking alcohol while taking this medicine can cause more severe side effects.

Further treatment

For some women, the first course of treatment doesn't treat BV effectively. 

If your initial treatment has been unsuccessful, your doctor will need to check you took the medicine correctly. If you did, you may be prescribed one of the different options described above.

If you have an intrauterine device (IUD) that may be contributing to your BV, your doctor may recommend having it removed and using an alternative form of contraception.

Vaginal pH correction treatments

Vaginal pH correction treatments are a relatively new way of treating BV. These usually involve applying a gel to the inside of your vagina that changes the acid balance, making it a less hospitable environment for harmful bacteria. Most vaginal pH correction treatments are available over the counter from pharmacists.

However, it's not clear how effective these treatments are for treating BV. Some studies have suggested they may help, whereas others suggest they're either ineffective or less effective than antibiotics.

Referral to a specialist

If you have repeated episodes of BV in a short space of time, your GP may refer you to a genitourinary medicine (GUM) specialist for further investigation and treatment.

If you're pregnant, you may be referred to your midwife or obstetrician (a specialist in pregnancies), who can discuss treatment options with you. 

Complications of bacterial vaginosis

For the vast majority of women, bacterial vaginosis (BV) is easily treated and doesn't cause any further problems. However, if the condition isn't treated, there's a small risk you may develop complications.

Pregnancy complications

There's some evidence to suggest untreated BV symptoms during pregnancy can increase your risk of pregnancy-related complications, particularly if you've had these problems in the past.

Pregnancy-related complications that have been associated with BV include:

  • premature birth – where the baby is born before the 37th week of pregnancy
  • miscarriage – the loss of pregnancy during the first 23 weeks
  • the amniotic sac breaking open too early – the amniotic sac is the bag of fluid where an unborn baby develops
  • chorioamnionitis – an infection of the chorion and amnion membranes (the membranes that make up the amniotic sac) and the amniotic fluid (the fluid that surrounds the foetus)
  • postpartum endometritis – infection and inflammation of the womb lining after giving birth, particularly after having a caesarean section

See your GP or visit a sexual health or genitourinary medicine (GUM) clinic as soon as possible if you're pregnant and have symptoms of BV. While your risk of developing these complications is small, treatment may reduce the risk.

If BV hasn't caused symptoms, there's no evidence to suggest it increases the risk of complications in pregnancy. Treatment might not be recommended if BV is detected while you're pregnant but don't have any symptoms.

Sexually transmitted infections

There's evidence that having BV can make you more at risk of catching sexually transmitted infections (STIs), such as chlamydia. This is possibly because the change in bacteria levels inside your vagina reduces your protection against infection.

Pelvic inflammatory disease

Although a link isn't entirely clear, some evidence suggests that BV may increase your risk of developing pelvic inflammatory disease (PID). PID causes infection and swelling of the upper female genital tract, including the womb, fallopian tubes and ovaries.

Symptoms of PID include:

  • pain around the pelvis or lower abdomen
  • discomfort or pain during sex felt deep inside the pelvis
  • bleeding between periods and after sex

If diagnosed at an early stage, PID can usually be treated successfully with a course of antibiotics. However, an estimated one in five women with the condition become infertile because of severe scarring on the fallopian tubes.

It's important to see your GP if you experience any symptoms of PID. Delaying treatment or having repeated episodes of PID can increase your risk of infertility.

In vitro fertilisation

Women who have BV and are using in vitro fertilisation (IVF) may have a lower success rate and an increased risk of early miscarriage.

If you're having IVF and have symptoms of BV, see your GP or speak to your infertility specialist.

Recurrent BV

It's relatively common for BV to recur after treatment with antibiotics. It's estimated that more than half the women treated for BV develop the condition again within three months.

If your BV returns, see your GP or sexual health or GUM clinic to discuss further treatment options.