Bacterial Vaginosis

What is bacterial vaginosis and what are the symptoms?

Bacterial vaginosis (BV) is a common condition of the vagina caused by an overgrowth of various bacteria (germs). It is not just a simple infection caused by one type of bacterium.

  • The main symptom of BV is a vaginal discharge. BV is one of the most common causes of vaginal discharge in women of childbearing age. The discharge is often a white-grey colour, and often has a fishy smell. The smell may be most noticeable when having sex. The discharge tends to be heaviest just after a period, and after having sex.
  • The discharge does not usually cause itch or soreness around the vagina and vulva.
  • Many women with BV do not have any symptoms (up to half of cases). BV may be found by chance when vaginal swabs are taken for other reasons.

Note: BV is not the only cause of a vaginal discharge. Various conditions can cause a discharge. For example, another common cause of a discharge is due to thrush (an infection caused by a yeast called candida). Unlike BV, thrush typically causes a thicker white discharge which tends to cause itch and soreness around the vagina and vulva. See separate leaflet called ‘Vaginal Thrush’ for more detail.

What causes bacterial vaginosis?

BV is not caused by a single bacterium (germ). In BV, an ‘overgrowth’ of various bacteria occurs in the vagina. It is not clear why this happens. Normally, there are various different types of harmless bacteria in the vagina. These bacteria help in the defence against harmful germs (such as candida which causes thrush). In BV, there is a change in the balance of the normal bacteria in the vagina, and certain bacteria multiply and thrive much more than usual. Some bacteria become much more prominent than they normally are.

Doctors describe these changes as “a change in the bacterial flora of the vagina from mainly lactobacillus species to high concentrations of anaerobic bacteria.”

BV is not caused by poor hygiene. In fact, excessive washing of the vagina may alter the normal balance of bacteria in the vagina, which may make BV more likely to develop.

Who gets bacterial vaginosis and how common is it?

About 1 in 3 women have BV at some time in their life. It may be much more common than this as many cases are mild and cause no symptoms. Any woman can be affected by BV. BV is more common in women who have an intra-uterine contraceptive device (IUD). It may also be more common in women who smoke. Hormone changes during your menstrual cycle as well as genetics may also play a part.

Is bacterial vaginosis a sexually transmitted disease?

No, BV can affect any woman, including those who do not have sex. However, BV is more common amongst sexually active women than non-sexually active women. No bacterium is passed on between sexual partners that causes this condition. Sexual partners of women with BV do not need any treatment. However, some cases of BV seem to be sexually ‘related’. It may develop after a change in sexual partner. In these cases, the infection is not ‘caught’ from anyone. But a change in sexual partner may affect the balance of normal bacteria in the vagina. BV is also more likely in women in same sex relationships who have had a change of partner.

How is bacterial vaginosis diagnosed?

The typical discharge and its characteristic fishy smell makes BV likely. In women in a regular, monogamous relationship, your doctor or nurse may be happy to diagnose BV just by your typical symptoms. However, there are some tests available that can help to confirm the diagnosis. Also, if you are pregnant, it is important to make an accurate diagnosis if you have vaginal discharge so that any infection can be treated effectively. This will mean having one or more of the tests below.

Testing the acid level of your vagina

The discharge of BV has a typical pH level (acid/alkaline balance) compared to other causes of discharge. (The overgrowth of the bacteria of BV causes the pH to change in the vagina so that it becomes more alkaline, ie the pH rises.) If available, your doctor or nurse may suggest that they take a sample of your discharge and test it with some pH paper. In addition, if an alkali is added to a sample of the discharge, it often causes a characteristic fishy smell.

Taking a sample (a swab)

To help clarify the diagnosis, your doctor or nurse may also suggest that a sample (a swab) of your discharge is taken from your vagina and sent to the laboratory for testing. Large numbers of various bacteria that occur with BV are seen under the microscope. Your doctor or nurse may suggest that they take more than one swab from your vagina to rule out other causes of vaginal discharge.

What are the possible complications with bacterial vaginosis?

BV and pregnancy

If you have untreated BV during pregnancy, you have an increased risk of developing some complications of pregnancy. For example, early labour, miscarriage, having a low birth weight baby or developing an infection of the uterus (womb) after childbirth.

BV and surgery

If you have untreated BV, the chance of developing an infection of the uterus is higher following certain operations. For example, following a termination of pregnancy or a vaginal hysterectomy. However, antibiotics are given before various operations of the uterus if you have BV. This can usually prevent these infections.

BV and other infections

If you have untreated BV, you may have an increased risk of developing HIV infection if you have sex with someone who is infected with HIV. There is also some evidence that women with untreated BV may be at an increased risk of developing pelvic inflammatory disease (PID). See separate leaflets called ‘Pelvic Inflammatory Disease’ for more details.

What is the treatment for bacterial vaginosis?

Not treating is an option for some women

BV often causes no symptoms, or the symptoms are mild. Also, there is a good chance that BV will gradually clear without treatment, as the balance of bacteria in the vagina may correct itself. So, if you have no symptoms or only mild symptoms, not treating is an option.

However, if you are pregnant and you are found to have BV but have no symptoms, you may still be advised to take antibiotic treatment. The benefits of treating pregnant women with BV and no symptoms is a little uncertain. Your doctor may seek advice from a gynaecologist about whether or not you need treatment.

Note: all pregnant women who have symptoms due to BV should be offered treatment. If you are found to have BV and are undergoing a termination of pregnancy, treatment with antibiotics may also be advised even if you have no symptoms. This is because there is a risk of BV causing a more serious infection of the uterus (womb) or pelvis after the procedure if it is not treated. Some doctors also suggest antibiotics for women who are about to undergo other gynaecological procedures (such as an endometrial biopsy – a biopsy of the lining of the womb) and are found to have BV but have no symptoms.


A course of metronidazole tablets is the common treatment. Metronidazole is an antibiotic. It clears BV in most cases. Read the leaflet that comes with the tablets for a full list of possible side-effects and cautions. However, main points to note about metronidazole include:

  • The usual dose is 400 mg twice a day for seven days. A single dose of 2 grams is an alternative, although this may be less effective and may cause more side-effects. (Note: this single dose is not recommended if you are pregnant.) If you are taking the 7-day course, it is important to finish the course and not to miss any tablets.
  • Some people feel sick, and may vomit when they take metronidazole. This is less likely to occur if you take the tablets straight after food. A metallic taste is also a common side-effect.
  • Do not drink any alcohol while taking metronidazole, and for at least 48 hours after stopping treatment. The interaction with alcohol can cause vomiting and other problems such as flushing and an increased pulse rate.
  • Breastfeeding: metronidazole can get into breast milk, but is not thought to affect breastfed babies. However, to play safe, the standard 7-day course with the 400 mg twice-daily dose is preferred so a baby does not get a large dose. If it is essential to use the 2 gram single dose, then it should be taken after the last breastfeed of the evening (at the start of the overnight breastfeeding break) to limit exposure to the baby.
  • Antibiotics used to treat BV may interfere with your contraceptive pill or patch. You should discuss this with the doctor or nurse who is treating you.

Alternative antibiotic treatments

Metronidazole vaginal gel or clindamycin vaginal cream placed inside the vagina can be used if you prefer this type of treatment, or have unpleasant side-effects with metronidazole tablets. The ability of these treatments to clear BV is about the same as metronidazole taken by mouth.

Note: as with metronidazole tablets, you should avoid alcohol while using metronidazole gel and for at least 48 hours after stopping treatment. Also, clindamycin vaginal cream can cause weakening of latex condoms and diaphragms. Therefore, during treatment and for five days after treatment with clindamycin vaginal cream, do not rely on condoms or diaphragms to protect against pregnancy and sexually transmitted diseases.

Other treatments

Overall, there is no strong evidence at the moment that live yoghurt or lactobacillus acidophilus are helpful in treating or preventing BV.

Do I need a ‘test of cure’

Women who are not pregnant

You do not need any further tests (such as swab tests) after treatment to ensure that BV has cleared (a ‘test of cure’) provided that your symptoms have gone.

Women who are pregnant

If you are pregnant, it is suggested that you do have a swab test taken after one month to ensure that BV is no longer present.

Treating recurrences

If you have a recurrence of symptoms and did not have any swab tests taken initially, your doctor or nurse may suggest that they take swab tests now. This is to confirm that it is definitely BV that is causing your symptoms.

BV may recur if you did not complete your course of antibiotics. However, even if you have completed your full course of antibiotics, BV recurs within three months in around 1 in 3 women. If it does recur, a repeat course of antibiotics will usually be successful in treating it. A small number of women have repeated episodes of BV, and need repeated courses of antibiotics.

If you have an intrauterine contraceptive device (IUD) and have recurrent BV, your doctor or nurse may suggest that they remove your IUD to see if this helps to improve your symptoms. You will need to discuss alternative contraception measures with them.

How can I prevent further episodes of bacterial vaginosis?

Most episodes of BV occur for no apparent reason, and cannot be prevented. However, the following are thought to help prevent some episodes of BV. The logic behind these tips is to try not to upset the normal balance of bacteria in the vagina:

  • Do not push water into your vagina to clean it (douching).
  • Do not add bath oils, antiseptics, scented soaps, perfumed bubble bath, shampoos etc, to bath water.
  • Do not use strong detergents to wash your underwear.
  • Do not wash around your vagina too often. Once a day is usually enough.

Further help and information

Women’s Health Concern

4-6 Eton Place, Marlow, Bucks SL7 2QA
Tel (helpline) Nurse Counselling Service: 0845 123 2319 (local rate)
Web: www.womens-health-concern.org
A leading charity providing help and advice to women on a wide variety of gynaecological, urological and sexual health conditions.



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