Bacterial vaginosis (BV) is an imbalance of the usual bacteria found in a woman’s vagina. It causes an abnormal vaginal discharge which can smell fishy and unpleasant.

The vagina

The vagina is a tube of muscle that runs from the cervix (the opening of the womb) to the vulva (the external sexual organs). Some types of bacteria are always present in the vagina to keep it healthy.

If a woman has BV, the usual balance of bacteria changes. The vagina will have:

• less lactobacilli (lactic acid bacteria)
• an overgrowth of other types of bacteria
• a higher pH (the measure of acidity and alkalinity), making it more alkaline

How common is bacterial vaginosis?

Bacterial vaginosis is the most common cause of abnormal vaginal discharge. In the UK, around 12-30% of women may be affected. Among pregnant women, this figure may be around 20%.

The cause of BV is not fully understood, although some factors make it more likely. While BV is not a sexually transmitted infection (STI), it is more common among people who are sexually active. Other factors that contribute to BV include smoking and using certain hygiene products.

Outlook

BV can appear and disappear without any reason, and around half of all women with BV are asymptomatic (do not have any symptoms). If there are no symptoms, treatment is not necessary. Where there are symptoms, antibiotics may be recommended.

Treatment is effective in up to 90% of BV cases, although it is quite common for BV to reoccur. Around 25% of women will have BV again within one month and will need to be treated with antibiotics again.

BV has been linked to a number of other conditions. It may increase the risk of having some STIs, such as gonorrhoea. Pregnant women with BV may also be at increased risk of developing complications, such as a preterm birth (when a baby is born before the 37th week of the pregnancy).

Around half of all women with bacterial vaginosis (BV) are asymptomatic. This means that they do not have any signs or symptoms. If you do not have symptoms, there is no need to get tested to find out if you have BV.

If you do have symptoms, you might notice a change in your usual vaginal discharge. Your discharge may:

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

BV does not usually cause itching or irritation.

See your GP as soon as possible if you have any abnormal discharge from your vagina. It is important to get bacterial vaginosis (BV) diagnosed to rule out other infections, such as trichomonas vaginalis or gonorrhoea. These can both cause abnormal vaginal discharge.

If you prefer, you could visit a sexual health clinic for a diagnosis, instead of your GP. Sexual health clinics are sometimes known as genito-urinary medicine (GUM) clinics. They are usually located in a hospital or are part of another health centre. Find your nearest sexual health service.

Examination

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, if you are sexually active and it is possible that you may have a sexually transmitted infection (STI) instead of BV, you may need to have some further tests. 

Tests

Your GP or healthcare professional will use a swab or a small plastic loop to collect a sample of cells from the walls of your vagina. A swab looks a bit like a cotton bud but is smaller, soft and rounded.

The swab or loop is used to pick 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 will be examined to check for BV. The result may be available immediately or the sample may be sent to a laboratory, in which case the result will usually be available within a week.

The pH (alkaline/acid balance) of your vagina may 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.

These tests and all sexual health services are free on the NHS. They are available to everyone, regardless of age.

Bacterial vaginosis (BV) can be treated with antibiotics. Several different antibiotics, which come in different forms, can be used. If used correctly, treatment is effective in 85-90% of cases.

There is currently no evidence that probiotics, such as those found in live yoghurt, are of any benefit for treating or preventing BV.

Metronidazole

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

• as tablets to be swallowed twice a day, for seven days
• as tablets to be taken as a single larger dose that you only take once
• as a gel that you apply to your vagina once a day, for five days

The most effective way to take metronidazole is in tablet form over seven days. This is also the preferred treatment if you are pregnant or breastfeeding. More people find that their BV is more likely to return if they choose to take the single larger dose.  

Warning

It is recommended that you do not drink alcohol while taking metronidazole and for 48 hours afterwards. This is because metronidazole can react with alcohol, causing you to feel very unwell.

Clindamycin

Clindamycin is an alternative antibiotic that may be prescribed for treating BV. It is available in two forms:

• as a cream that you apply to your vagina once a day for seven days
• as capsules that you swallow twice a day, for seven days

The capsules are rarely used nowadays as they have been linked to a serious side effect called pseudomembranous colitis. This is severe inflammation (swelling) of the inner lining of the colon (large intestine).

Warning

Clindamycin cream can weaken barrier methods of contraception, such as latex condoms, diaphragms and caps. This means that they will not be effective at preventing pregnancy and will not protect you against sexually transmitted infections (STIs).

You will need to use additional contraception and protection against STIs while you are using clindamycin cream and for five days afterwards. Some types of condom, such as those made from polyurethane, may still work. Ask your GP for advice.

Tinidazole

Tindiazole is an alternative medication that may be prescribed, although its effect on bacterial vaginosis has been less well studied. Tinidazole is taken orally (by mouth) as a single dose. As with metronidazole, you should not drink alcohol while you are taking this medication.

After treatment

If your BV symptoms disappear after treatment, you will not need to be tested for BV again to confirm that the treatment has worked. However, you will need to be tested if:

• your signs and symptoms do not go away
• your signs and symptoms return, or
• you are treated for BV while you are pregnant

Further treatment

The first course of treatment may not be effective in around 10-15% of people. If your treatment has been unsuccessful, your GP will need to check that you took the medicine correctly. If you did and it did not work, you may be prescribed one of the different options described above.

Alternatively, you may be referred to a gynaecologist (a specialist in treating conditions of the female reproductive system). If you are pregnant, you may be referred to an obstetrician (a specialist in pregnancies). They will be able to discuss further treatment options with you.  

Bacterial vaginosis (BV) has been linked to a number of other conditions. It is thought that BV may contribute to:

• pelvic inflammatory disease (PID), a condition that involves infection and inflammation (swelling) of the upper female genital tract

• tubal factor infertility, caused by damage to the fallopian tubes (the tubes that connect the ovaries to the womb)

Sexually transmitted infections

There is also evidence of a link between BV and some sexually transmitted infections (STIs). If you have BV, you may be at more risk of:

• gonorrhoea
• chlamydia
• genital herpes
• HIV and AIDS
• becoming infected with the human papilloma virus (HPV). This causes abnormal tissue growth and other changes to cells, which can lead to genital warts or cervical cancer

Pregnant women

Pregnant women who have BV may be at higher risk of:

• a late miscarriage (the loss of pregnancy
• the amniotic sac (the bag of fluid where the unborn baby develops) breaking open too early
• preterm birth, where the baby is born before the 37th week of pregnancy
• 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 - irritation or inflammation of the lining of the womb (uterus) after giving birth 

If you are pregnant and have symptoms of BV, see your GP immediately. BV can be safely treated when you are pregnant or breastfeeding.

The National Institute for Health and Clinical Excellence (NICE) does not recommend that you are tested for BV if you are pregnant and do not have any symptoms (asymptomatic). This is because there is no evidence that treating asymptomatic pregnant women lowers their risk of pregnancy-related complications.

In-vitro fertilisation

Women who have BV and are using in-vitro fertilisation (IVF), a technique to help couples with fertility problems, may have:

• a lower success rate
• 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

After being successfully treated for BV, around 20-25% of women may find that the condition returns within one month. Over time, BV may reoccur in up to 80% of women. If your BV reoccurs, return to your GP to discuss further treatment options.

The causes of bacterial vaginosis (BV) are not fully understood, so it is not possible to completely prevent it. However, you may be able to lower your risk of developing BV if you stop:

• using scented soaps and perfumed bubble bath
• using vaginal deodorant
• douching (washing or cleaning out your vagina)
• putting antiseptic liquids in the bath
• 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.

Safer sex

Although BV is not sexually transmitted, many infections are. If you are sexually active, having safe sex offers you and your partner the best protection against sexually transmitted infections (STIs).

Following the advice below will enable you to have a safer sex life:

• Keep the number of sexual partners that you have to a minimum.
• Use a barrier method of contraception, such as condoms, every time you have vaginal or anal sex.
• If you have oral sex, cover the penis with a condom or the female genitals with a latex, or polyurethane (plastic), square (dam).
• Find out how to use a condom.
• Avoid sharing sex toys. If you do share them, make sure that you wash them or cover them with a new condom before anyone else uses them.

You and your partner(s) should have regular check-ups for sexually transmitted infections (STIs). This can be done at your GP surgery or at a sexual health clinic (GUM clinic).

These measures can help protect you against STIs or, if you have an STI, will prevent you from passing it on to your partner.