Bacterial vaginosis (BV) is common and causes a vaginal discharge, often with a noticeable smell. BV is not a sexually transmitted infection. It is caused by an overgrowth of normal germs (bacteria) in the vagina. Symptoms are often mild, and BV may clear without treatment. Other cases can be treated with antibiotic medication.
What is bacterial vaginosis (BV) and what causes it?
BV is a common condition of the vagina caused by an overgrowth of various germs (bacteria). It is not just one simple infection caused by one type of germ (bacterium). The vagina normally has a mix of bacteria, but in BV the balance changes. It is not clear why this happens. As a result, certain bacteria multiply and thrive much more than usual. Some bacteria become much more prominent than they normally are.
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 (BV) and how common is it?
It is not exactly known how common BV is, because it is often so mild that women may not go to the doctor. It may be that as many as about 1 in 3 women have BV at some time in their lives.
You are more likely to get BV if:
- You are sexually active. (Women who have never had sex can get BV too. However, it is more common in women who are having sex. You can have BV whether you have sex with women or with men.)
- You have recently changed your sexual partner.
- You have a past history of sexually transmitted infections (STIs).
- You smoke.
- You have a copper coil for contraception - an intrauterine contraceptive device (IUCD).
- Your family has Afro-Caribbean origins.
- You use bubble bath.
You are less likely to get BV if:
What are the symptoms of bacterial vaginosis (BV)?
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 white-grey in colour, and often has a fishy smell. The smell may be more noticeable during sex. The discharge tends to be heaviest just after a period, or after 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).
Note: BV is not the only cause of a vaginal discharge. Various conditions can cause discharge. For example, another common cause of vaginal discharge is an infection caused by a yeast called thrush (candida). Unlike BV, thrush typically causes a thicker white discharge which tends to cause itching and soreness around the vagina and vulva. (See separate leaflet called Vaginal Thrush for more information.) STIs, such as chlamydia, may also cause vaginal discharge. (See separate leaflet called Genital Chlamydia for more information.)
Is bacterial vaginosis (BV) a sexually transmitted disease?
No, BV can affect any woman, including those who do not have (or who have never had) sex. However, BV is more common amongst sexually active women than amongst non-sexually active women. No germ (bacterium) is passed on between sexual partners to cause 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 germs (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 (BV) diagnosed?
The typical discharge and its characteristic fishy smell make BV likely. If you are in a stable, long-term relationship, your doctor or nurse may be happy to diagnose BV just by it's 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 germs (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 confirm the diagnosis, your doctor or nurse may also suggest that a swab of your discharge be 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 of bacterial vaginosis (BV)?
BV and pregnancy
If you have untreated BV during pregnancy, you have a slightly increased risk of developing some complications of pregnancy. These include:
- Early labour.
- Having your baby early (preterm birth).
- Having a low birth-weight baby.
- Developing an infection of the womb (uterus) after childbirth (postpartum endometritis).
BV and surgery
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. You may also be more likely to pass on HIV if you have HIV and BV together. 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 HIV and AIDS and Pelvic Inflammatory Disease.)
What is the treatment for bacterial vaginosis (BV)?
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. Any disruption in the balance of vaginal germs (bacteria) may be corrected naturally, with time. So, if you have no symptoms or only mild symptoms, you may not need any treatment.
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 benefit of treating pregnant women who have 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 do not have any symptoms. This is because there is a risk of BV causing a more serious infection of the womb (uterus) or pelvis after the procedure if it is not treated. Some doctors also suggest antibiotics for women with BV (and no symptoms) who are about to undergo other gynaecological procedures such as an endometrial biopsy - a biopsy of the lining of the womb.
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 400-500 mg twice a day for 5-7 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 seven-day course, it is important to finish the course and not to miss any tablets.
- Some people feel sick or may be sick (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.
- Breast-feeding: metronidazole can get into breast milk but will not harm your baby. However, oral metronidazole is not recommended and instead you should use vaginal metronidazole or clindamycin.
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, vaginal creams and gels 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 STIs.
Overall, there is no strong evidence at the moment that live yoghurt or Lactobacillus acidophilus (found in certain commercial probiotic products) is helpful in treating or preventing BV. Antiseptics and disinfectants do not help treat BV.
Do I need a test of cure?
Women who are not pregnant
After treatment, you do not need any further tests 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 test one month after treatment to ensure that BV is no longer present. A sample of the discharge in your vagina (a swab) is taken. This is tested to check you no longer have BV.
If you have a recurrence of symptoms and did not have a test using a sample of your vaginal discharge (a swab) taken initially, your doctor or nurse may suggest that they take swab tests now. This is to confirm that it is BV causing your symptoms.
BV may return (recur) if you did not complete your course of antibiotics. However, even if you have completed a full course of antibiotics, BV recurs within three months in many women. If it does recur, a repeat course of antibiotics will usually be successful. A small number of women have repeated episodes of BV, and need repeated courses of antibiotics.
If you have a copper coil for contraception - an IUCD - and have recurrent BV, your doctor or nurse may suggest that they remove your IUCD 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 (BV)?
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 germs (bacteria) in the vagina:
- Do not push water into your vagina to clean it (douching). The vagina needs no specific cleaning.
- 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 and vulva too often. Once a day is usually enough.
Further reading & references
- Management of bacterial vaginosis; British Association for Sexual Health and HIV (May 2012)
- Brotman RM, Ghanem KG, Klebanoff MA, et al; The effect of vaginal douching cessation on bacterial vaginosis: a pilot study. Am J Obstet Gynecol. 2008 Jun;198(6):628.e1-7. Epub 2008 Mar 4.
- Bacterial vaginosis; NICE CKS, May 2013 (UK access only)
- Oduyebo OO, Anorlu RI, Ogunsola FT; The effects of antimicrobial therapy on bacterial vaginosis in non-pregnant women. Cochrane Database Syst Rev. 2009 Jul 8;(3):CD006055. doi: 10.1002/14651858.CD006055.pub2.
- Brocklehurst P, Gordon A, Heatley E, et al; Antibiotics for treating bacterial vaginosis in pregnancy. Cochrane Database Syst Rev. 2013 Jan 31;1:CD000262. doi: 10.1002/14651858.CD000262.pub4.
- Sexually Transmitted Infections in Primary Care; Royal College of General Practitioners and British Association for Sexual Health and HIV (Apr 2013)
- Senok AC, Verstraelen H, Temmerman M, et al; Probiotics for the treatment of bacterial vaginosis. Cochrane Database Syst Rev. 2009 Oct 7;(4):CD006289.
- Evans AL, Scally AJ, Wellard SJ, et al; Prevalence of bacterial vaginosis in lesbians and heterosexual women in a community setting. Sex Transm Infect. 2007 Oct;83(6):470-5. Epub 2007 Jul 4.
- Vaginal discharge; NICE CKS, May 2013 (UK access only)
Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.
Dr Tim Kenny
Dr Mary Harding
Dr Hannah Gronow