Bacterial vaginosis

It's not a sexually transmitted infection but can develop after you've had sex.

Bacterial vaginosis (BV) is the most common cause of unusual vaginal discharge. One in three people with a vagina get it at some time. People with a penis don’t get bacterial vaginosis.

It's not a sexually transmitted infection but can develop after you've had sex.

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  • Around half of people with bacterial vaginosis won’t have any signs and symptoms at all, or may not be aware of them.
  • You might notice a change in your usual vaginal secretions (discharge). This may increase, become thin and watery, change to a white/grey colour and develop a strong, unpleasant, fishy smell, especially after sex.
  • Bacterial vaginosis isn’t usually associated with soreness, itching or irritation.

The cause of bacterial vaginosis (sometimes called BV) isn’t really understood. People who have bacterial vaginosis have:

  • less normal vaginal bacteria (lactobacilli)
  • an overgrowth of other types of bacteria in the vagina
  • a change in pH (acid/alkaline balance) of the vagina with the vagina becoming more alkaline.

Bacterial vaginosis is more common if you:

  • use medicated or perfumed soaps, bubble bath or shower gel
  • put antiseptic liquids in the bath
  • douche or use vaginal deodorant
  • use strong detergents to wash your underwear
  • smoke.

Hormonal changes during the menstrual cycle, receiving oral sex, semen in the vagina after sex without a condom, an intrauterine contraceptive device (IUD) and genetic factors may also play a part.

Bacterial vaginosis isn’t a sexually transmitted infection, but people with a vagina who are sexually active and have had a change of partner are more likely to have it, including those in same-sex relationships.

If you think you may have it, talk to a doctor or nurse who might recommend a test if you have signs and symptoms.

You may notice these yourself or they may be noticed by a doctor or nurse during a vaginal examination.

You may be offered a test during pregnancy if you have symptoms. You should be offered a test before some gynaecological procedures and before an abortion.

Bacterial vaginosis isn’t a sexually transmitted infection but it’s important you don’t delay getting advice if you may have been at risk of a sexually transmitted infection.

What does the test involve?

A doctor or nurse may examine inside of your vagina to look at any vaginal discharge and to collect a sample from the vaginal walls using a swab. A swab looks like a cotton bud, but is smaller and rounded. It sometimes has a small plastic loop on the end rather than a cotton tip. It only takes a few seconds to wipe over the area and isn’t usually painful, though it may be uncomfortable for a moment.

The pH (alkaline/acid balance) of the vagina may be measured by wiping a sample of vaginal discharge over a piece of specially treated paper.

Sometimes your test result will be available straight away, but other times it can take up to two weeks.

Sometimes bacterial vaginosis is noticed during a cervical screening test (smear test), but you’ll only need treatment if you have problems with discharge. Routine blood tests don’t detect infections such as bacterial vaginosis.

It’s also possible to buy a bacterial vaginosis test to do at home. If you buy a testing kit, get advice from a pharmacist or your doctor.

It’s not always necessary to have a test for bacterial vaginosis.

How accurate are the tests?

The accuracy of a bacterial vaginosis test depends on the test used and the type of sample that’s collected. Microscopy tests (where a sample is looked at with a microscope) for bacterial vaginosis are usually accurate. 

Where can I get a test?

There are a number of services you can go to. Choose the one you feel most comfortable with.

A test can be done at:

  • your general practice
  • some contraception clinics and young people’s services
  • a genitourinary medicine (GUM) or sexual health clinic
  • Treatment for bacterial vaginosis is simple and involves taking antibiotic tablets. There are several different antibiotics that can be used. These are taken either as a single dose or a longer course (up to one week).
  • You may be given a cream or gel instead. You’ll need to use this in the vagina for 5–7 days.
  • The doctor or nurse will advise you how to use the treatment. If you’re given the antibiotic metronidazole, either as tablets or a vaginal gel, you’ll be advised not to drink alcohol during the treatment and for 48 hours afterward. This is because it reacts with alcohol and can make you feel very unwell.
  • Some creams can weaken latex condoms, diaphragms and caps. Polyurethane (soft plastic) types can be safely used. Ask the doctor or nurse for advice.
  • Tell the doctor, nurse or pharmacist if you’re pregnant, think you might be, or you’re breastfeeding. This can affect the type of treatment you’re given.

How effective is the treatment?

Treatment is effective if used correctly. It’s quite common for bacterial vaginosis to return, and some people get it multiple times.

Do I need to have a test to check that the bacterial vaginosis has gone?

You only need another test if:

  • signs and symptoms don’t go away
  • signs and symptoms come back.

What happens if bacterial vaginosis isn’t treated?

For many people, bacterial vaginosis goes away by itself.

If your partner has a vagina, they should get advice from a doctor or nurse about whether they need treatment.

What can be done if bacterial vaginosis keeps coming back?

We don’t know why bacterial vaginosis keeps recurring in some people.

There’s no agreed preferred way of treating recurrent infection. Some people may be given a course of antibiotic gel to use over a number of months. Others may be given antibiotic tablets to use at the start and end of their period. Some people may find it helpful to use a lactic acid gel (available from a pharmacy) to restore the pH balance in the vagina.

Ask your doctor, nurse or pharmacist for advice

Will bacterial vaginosis affect my chances of getting pregnant?

No. There's no evidence that bacterial vaginosis will affect your chances of getting pregnant.

Bacterial vaginosis during pregnancy

  • Bacterial vaginosis may cause problems with a pregnancy. It's been found in some people who have had a miscarriage, a premature birth or a low birth weight baby.
  • Bacterial vaginosis can safely be treated when you're pregnant and when you're breastfeeding – this won’t harm the baby. Do tell the doctor or nurse if you're pregnant or breastfeeding as it may affect the treatment you're given.

Does bacterial vaginosis cause cervical cancer?

No. Bacterial vaginosis doesn't cause cervical cancer.

BV isn't a sexually transmitted infection, although it can develop after you have sex.

It's possible to get a sexually transmitted infection (STI) by having sex with someone who has an STI, even if they have no symptoms.

The following measures will help protect you from most STIs including chlamydia, gonorrhoea and HIV.

If you have a sexually transmitted infection they’ll also help prevent you from passing it on to someone else.

  • Use condoms (external/male or internal/female) every time you have vaginal or anal sex.
  • If you have oral sex, use a condom to cover the penis, or a latex or polyurethane (soft plastic) square to cover the anus or female genitals.
  • Avoid sharing sex toys. If you do share them, wash them or cover them with a new condom before anyone else uses them.
  • How to use condoms.
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This website can only give you general information. The information on this page is based on evidence-based guidance produced by The British Association for Sexual Health and HIV (BASHH) and The Faculty of Sexual and Reproductive Healthcare of the Royal College of Obstetricians and Gynaecologists.

Contact your doctor, practice nurse or a clinic if you are worried or unsure about anything.