What are the symptoms of bacterial vaginosis (BV)?

Bacterial vaginosis may not actually cause any symptoms. However it is the commonest cause of abnormal vaginal discharge in women, causing a thin white or greyish white discharge. There is also a characteristic fishy smell, which can be more noticeable after sex. There is no irritation, inflammation, or itch with BV, but these may be caused by other infections which can be present alongside BV.

Also see NHS - Bacterial vaginosis.

What causes BV?

BV is believed to be caused by a change in the natural balance of bacteria in the vagina. There is a change in the acid balance and the vagina becomes less acidic. The usually dominant lactobacilli are overshadowed by other anaerobic bacteria. Anaerobic bacteria do not require oxygen. These bacteria produce a characteristic unpleasant fishy smell, and there is a thin white or greyish white discharge. There is no irritation, inflammation, or itch with BV and many women actually have no symptoms at all.

What is the natural vaginal pH?

A healthy vagina is naturally slightly acidic, with a pH below 4.5. In BV the pH shifts higher to between 4.5 and 6.

What is the role of lactobacilli in BV?

Lactobacilli are the 'friendly' bacteria which are usually dominant in the vagina. They produce hydrogen peroxide and lactic acid, causing the normal, slightly acidic, vaginal conditions. This acidity deters growth of the anaerobic bacteria found in BV. Products are available which treat BV with intravaginal lactobacillus or other probiotics, but trials have not shown consistent good results.

What bacteria are found in BV?

The bacteria found in BV are also found in the normal healthy vagina but in much lower numbers than when there is BV. They include Gardnerella vaginalis, Prevotella, Atopobium vaginalis, Peptostreptococcus, Bacteroides, Mycoplasma, Mobiluncus, Clostridiales, and Sneathia (formerly Leptotrichia).

How is BV diagnosed?

A laboratory diagnosis involves assessing the vaginal discharge under a microscope, checking vaginal pH and also testing the discharge with alkali solution. Results are then assessed using the Amsel, Nugent or Hay/Ison criteria.

In practice, a diagnosis is often made when there is a characteristic discharge and fishy smell. It can be confirmed by adding alkali (potassium hydroxide) to some discharge on a microscope slide, releasing the fishy smell.

Should I buy a self test kit to check for BV?

BV does not always require treatment, and will often settle spontaneously, and testing is not often necessary.

There are two types of self test kit available. The simplest are basic pH assessment swabs which indicate if the vaginal pH is higher than 4.5. More expensive tests check for traces of bacterial antigens and often combine testing for gardnerella vaginalis and trichomonas vaginalis (TV) infections or other infections.

Measuring the vaginal pH can be a useful indicator of BV, but if you have the characteristic symptoms and have previously had BV confirmed by a doctor, there is no need for a confirmatory test.

The bacterial antigen test looking for gardnerella vaginalis, is less reliable in testing for BV, as small numbers of gardnerella are also found in the healthy vagina. Trichomonas vaginalis infection is a sexually transmitted infection (BV is NOT sexually transmitted) and is often linked with having other sexually transmitted infections. If TV is found, it is recommended to attend a sexual health clinic for a full check for all STIs, including gonorrhoea.

Are there any risk factors for developing BV?

BV is found more commonly in:

  • Smokers.
  • Recent change in sexual partner.
  • Black women.
  • After receptive cunnilingus.
  • Alongside STIs such as herpes or chlamydia.

Factors which may alter vaginal pH are also linked to BV. These include vaginal douches and washes, vaginal deodorants, menstruation, sexual activity and semen in vagina, bubble baths, and copper IUD.

How can I protect against BV?

BV is less common in women who use the combined contraceptive pill as the oestrogen encourages lactobacilli. Using condoms and having a circumcised male partner are also protective.


  • Take a shower instead of a bath.
  • Use only water and a plain soap or aqueous cream to wash the genital area.
  • Do not use antiseptic, perfumed soap, bubble baths, shampoo, or shower gel in the bath.
  • Do not use vaginal douches and washes or vaginal deodorants.
  • Do not use strong detergent to wash underwear.
  • Do not smoke.
  • Reduce other avoidable risk factors.

How is BV usually treated?

There are several alternative prescription treatments for BV:

Most treatments have been shown to be equally effective with 70-80% cure rates. However the large one-off dose of 2 grams of oral metronidazole was slightly less effective in trials and is more likely to cause side effects.

Always use medication according to the regime actually prescribed for you.

Do I have to treat BV?

Many women with BV do not have any troublesome symptoms and do not need treatment. Often the vaginal acid and bacteria balance will normalise again on its own within the course of a monthly cycle, and any symptoms will settle down.

Is BV a sexually transmitted infection (STI)?

BV is not actually an STI as it is not passed between partners. It is a problem of acid balance not of one particular infection. It can be made worse by sex, because semen also alters the normal vaginal acid balance.

Should my partner be treated as well?

BV is not actually a sexually transmitted disease despite its link with sexual activity. Most studies have not shown any benefit from treating male partners. However, in a lesbian relationship the partner may also be affected by BV, and treating both women is often recommended.

I have a copper coil/IUD and keep getting BV - what can I do?

Sometimes the copper coil/IUD can be linked with recurrent episodes of BV. You should reduce avoidable risk factors and follow advice about protecting against BV.

If BV still keeps coming back, you should discuss switching to a different type of contraception with your sexual health provider and having the copper coil/IUD removed. A hormone releasing coil/IUS does not increase the risk of BV.

Can I treat BV with lactobacilli or lactic acid?

It is possible to buy products containing probiotic lactobacilli or lactic acid to use vaginally to treat BV. Some women find that they help, but medical trials have not shown consistent improvements.

Can I treat BV during my monthly 'period' (menses)?

BV is often triggered during menstruation, as the vaginal pH balance is affected by the bleeding - blood pH is 7.4. The manufacturer advises that Zidoval gel should not be used during the monthly period. Similarly Dalacin cream is better avoided whilst menstruating. Sometimes BV symptoms settle after the period, and it may be better to wait before treating. However metronidazole tablets can be safely and effectively used whilst having a 'period' (menses).

Will metronidazole affect my contraceptive pill?

No. Metronidazole should not affect the combined contraceptive pill, unless it causes you to actually vomit. In the past, doctors advised using extra precautions (condoms) when taking antibiotics alongside any contraceptive pills, but research has shown that most antibiotics have no effect on hormonal contraception. If metronidazole causes you to vomit within 3 hours of taking your contraceptive pill, follow the missed/vomited pills guidance.

See also will antibiotics stop my contraceptive working? and NHS - Common questions about metronidazole - Will it affect my contraception?

What problems does BV cause in pregnancy?

There is an association between having BV and being at higher risk of problems in late pregnancy including late miscarriage, preterm (early) birth, premature rupture of membranes, and postpartum endometritis (womb infection after giving birth). Also, babies may be born with lower than usual birth weight. It is not clear from research, whether treatment is actually beneficial in pregnancy but some obstetricians offer treatment for BV, if there are other risks that may trigger a preterm birth.

What treatment can I use for BV during pregnancy?

If BV needs to be treated during pregnancy, Zidoval and metronidazole tablets can be used at any time with caution. Taking metronidazole tablets has not been shown to harm pregnancies. However, the single high dose of metronidazole 2 grams is not recommended in pregnancy.

There is no clear data about the safety of Dalacin in the first trimester and manufacturers recommend only using it in the second and third trimesters, after 13 weeks.

Dr Fox does not prescribe during pregnancy.

What treatment can I use for BV whilst breastfeeding?

BV should be treated with vaginal cream or gel if breastfeeding. Metronidazole from tablets will pass into breast milk and can affect its taste. Zidoval vaginal gel containing metronidazole can be used with caution. Very little clindamycin from Dalacin vaginal cream is expected to get into breast milk but clinical trials have not actually been done. Clindamycin in tablets may potentially cause gut problems in the breastfed baby, so the manufacturers advise caution, even if using the cream.

Dr Fox does not prescribe for breastfeeding women.

Why are you more likely to catch sexually transmitted infections if you have BV?

Sexually transmitted infections (STIs) including HIV and pelvic inflammatory disease (PID) are more common in women with BV. This is probably because the healthy slightly acidic vagina prevents the growth of organisms which cause STIs. The less acidic environment with BV enables the STI organisms to survive.

How does metronidazole work?

Metronidazole passes into the anaerobic bacterial cells where the bacteria's own processing system converts it into a nitroso-radical. This radical poisons the cell, causing bacterial cell death.

Why does metronidazole make urine darker?

This is actually quite a rare side effect of metronidazole, but can be quite disconcerting. The urine can become Coca-cola coloured. It is not known exactly why this happens in some people, but it is thought to be caused by one of the breakdown products of metronidazole, possibly an azometabolite.

Do I really have to abstain from alcohol taking/using metronidazole?

For many years doctors have advised patients to avoid alcohol when taking metronidazole, as it is thought to cause a 'disulfiram' reaction. Disulfiram is given to people with alcoholism, to help them to stop drinking alcohol. Disulfiram inhibits the enzyme acetaldehyde dehydrogenase which leads to a bad reaction when alcohol is taken. The disulfiram reaction includes nausea, vomiting, dizziness, chest, head, and abdominal pains.

In recent years, research has shown that metronidazole does not have the same biochemical effect which causes the disulfiram reaction, and so the advice to abstain from alcohol is probably unnecessary. Despite this, the advice to avoid alcohol when taking metronidazole, and for 48 hours afterwards, is still usually given.

Does metronidazole affect blood test results?

Yes. If you are having blood tests let your doctor know that you have been taking metronidazole. It can affect liver tests, triglyceride tests and some glucose tests and may cause false values of zero.

Can I keep using the same treatment for BV if it keeps coming back?

Unfortunately in some women BV does keep recurring.

If it recurs very quickly, then tests for sexually transmitted infections should be taken. In particular trichomonas vaginalis infection may give similar symptoms, though usually with a frothy, smelly discharge and vulval soreness.

BV may recur repeatedly, requiring multiple treatments. Sometimes suppressive treatment is suggested, but there is no clear consensus of the best medication to use. Trials of a variety of different suppressive regimes have shown varying success but this is often not sustained long term.

Dr Fox offers up to one BV treatment every 3 months. Please consult your GP if you are having more frequent episodes.

Does Vitamin D stop BV?

No, unfortunately not. Women with BV often have low Vitamin D levels. However, a 2014 study on taking high dose vitamin D supplements and so restoring Vitamin D levels to normal, did not reduce the frequency of getting BV.

If the cure rate is only 70-80%, how do I know if the treatment has worked?

Treating BV is only recommended if there are troublesome symptoms, therefore if you don't have ongoing symptoms, then the BV can be assumed to have settled.

What do I do if the treatment doesn't work or my symptoms come back again very quickly?

If the symptoms of BV don't resolve with treatment, you will need to have tests for other causes of vaginal discharge including STIs. Consult your regular doctor or a sexual health clinic. If these tests are negative then an alternative BV treatment may be offered. Sometimes a regular suppressive treatment is required for women who develop frequent episodes of BV (more than 4 episodes per year).

Can BV be transmitted to men?

No. Men cannot have BV and studies haven't shown that they can pass it on. BV is not a sexually transmitted infection. In fact it is an imbalance of naturally occurring bacteria within the vagina. In BV, the vaginal pH becomes less acidic, the normally dominant lactobacilli are replaced by other anaerobic bacteria which cause the symptoms. BV can be made worse by sex, because semen also alters the normal vaginal acid balance.

Bacterial vaginosis treatment

Dr Amanda Wood

Authored 22 May 2023 by Dr A. Wood
MB ChB Manchester University 1984. Former NHS GP in Bristol. GMC no. 2855422

Reviewed by Dr C. Pugh, Dr B. Babor
Last reviewed 22 May 2023
Last updated 19 July 2024