Bacterial vaginosis


Bacterial vaginosis


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

BV does not usually cause any vaginal soreness or itching, but it often causes unusual vaginal discharge. If you have the condition, your discharge may:

develop a strong fishy smell, particularly after sexual intercourse

become a white or grey colour

become thin and watery

BV is not 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. In these cases, the condition does not pose any threat to your health or pregnancy.


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 are pregnant. It is important to get this checked to rule out other infections and prevent complications.

Your doctor will ask you about your symptoms and they 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.



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 is not classified as a sexually transmitted infection (STI), but you are at a higher risk of developing the condition if you are sexually active.

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

There is no evidence to suggest that 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 using scented soaps or bubble baths, having an intrauterine device (IUD) fitted and using vaginal deodorant. BV is more common in women who use a coil for contraception and those who perform vaginal douching (cleaning out the vagina).


Treating bacterial vaginosis

BV can usually be successfully treated using a short course of antibiotic tablets or an antibiotic gel that 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 is common for BV to recur. More than half of women successfully treated with BV will find their symptoms return, usually within three months. Women who have frequent episodes of BV may be referred to a genitourinary medicine (GUM) specialist.



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 in women who have had these complications in an earlier pregnancy. BV causes no problems in the great majority of pregnancies.

As a precaution, you should contact your GP or GUM clinic if you are 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.


Preventing bacterial vaginosis

The causes of bacterial vaginosis are not fully understood, so it is 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 will develop BV.


Causes of bacterial vaginosis 

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

Your vagina should contain bacteria called lactobacilli. These bacteria 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 is not as acidic as it should be. This allows other types of bacteria to grow.

It is still unclear what causes this change in the balance of bacteria, 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


use scented soaps, antiseptic bath liquids or bubble bath

clean out your vagina with water or other fluids (douching)

use vaginal deodorant

use strong detergents to wash your underwear

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


Is bacterial vaginosis an STI?

Bacterial vaginosis is generally not considered to be a sexually transmitted infection (STI). However, there is conflicting evidence on this issue.

Evidence that suggests that 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 is also evidence that women with BV can pass the condition to women they have sex with, although exactly how this happens is still unclear.

However, there is also evidence that suggests that BV may not be an STI:

there is no equivalent of BV in men

treating male partners with antibiotics does not prevent the recurrence of BV

rates of BV can vary significantly in different ethnic groups, which cannot be explained by sexual activity alone

BV can sometimes occur in women who are not sexually active

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


Can I pass it on to my partner?

There's no evidence that the bacteria causing bacterial vaginosis (BV) will affect male sexual partners.

However, some evidence suggests that women with BV may be able to pass the condition on to female sexual partners.

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 see your GP or visit a GUM clinic so it can be determined whether you have bacterial vaginosis (BV) or a similar condition, such as trichomoniasis or gonorrhoea. These can both also cause abnormal vaginal discharge.



Your GP or healthcare professional may diagnose BV from a description of your symptoms and by examining your vagina. In particular, they will 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 are 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 is not 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 is currently no evidence that probiotics, such as those found in some yoghurts, are of any benefit in treating or preventing BV.


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

tablets to be taken twice a day for five to seven days

a single larger-dose tablet you take only once

a gel that 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 are considered to be the most effective treatment. These can be taken if you have symptoms of BV while you are pregnant.

If you are 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 have had a reaction to metronidazole in the past, for example.

Whichever course of antibiotics you are prescribed, it is important to finish the course, even if you have started to feel better. This will help reduce the risk of symptoms persisting or recurring.


Side effects 

Metronidazole can cause nausea, vomiting and a slight metallic taste in your mouth. It is 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.

Do not 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

In some women, the first course of treatment does not effectively treat BV.

If your initial treatment has been unsuccessful, your doctor will need to check that 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 your doctor thinks may be contributing to your BV, they 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 is not clear how effective these treatments are for treating the condition. Some studies have suggested they may help treat BV, whereas others suggest they are either ineffective or less effective than treatment with antibiotics.


Referral to a specialist

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

If you are pregnant, you may be referred to your midwife or obstetrician (a specialist in pregnancies). They will be able to discuss treatment options with you. 


Things to avoid during treatment

While you are being treated for bacterial vaginosis (BV), there are some things you should avoid to reduce the chances of treatment being unsuccessful.

For example, you should avoid cleaning the inside of your vagina (douching) or using antiseptics, scented soaps and bubble baths in the bath.


Complications of bacterial vaginosis 

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

Pregnancy complications

There is some evidence to suggest that untreated bacterial vaginosis causing symptoms during pregnancy can increase your risk of pregnancy-related complications, particularly if you have 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 lining of the womb after giving birth

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

If BV hasn't caused symptoms, there is no evidence to suggest it will increase the risk of complications in pregnancy. Treatment may therefore not be recommended if BV is detected while you are pregnant but you don't have any symptoms.


Sexually transmitted infections (STIs)

There is evidence that having BV can make you more at risk of catching 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 is not entirely clear, some evidence suggests BV may increase your risk of developing a condition called pelvic inflammatory disease (PID). PID involves infection and inflammation (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 will 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 for PID or having repeated episodes of PID can increase your risk of infertility.


In vitro fertilisation (IVF)

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 are having IVF and have symptoms of BV, see your GP or speak to your infertility specialist.


Recurrent BV

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

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

Bacterial vaginosis