What is bacterial vaginosis?

Bacterial vaginosis (BV) is the most common vaginal infection in women in their reproductive years. About 1 in 3 women will have bacterial vaginosis at least once.

BV develops when there’s an overgrowth of bad bacteria (anaerobic bacteria), and a decrease in your good bacteria (lactobacilli).

This can cause your discharge to change colour and develop an unpleasant odour.

It isn’t a sexually transmitted infection (STI), but it's considered to be sexually associated as it can sometimes be passed on to other women during sex. Men can’t catch BV.

What causes bacterial vaginosis?

Different types of bacteria normally live on your vagina in harmony, but sometimes the lactobacilli and anaerobic bacteria can fall out of balance – usually if something changes the acidity of your vagina.

The normal pH of your vagina is 3.8–4.5, which is slightly acidic, because the lactobacilli produce lactic acid. If the pH goes above 4.5, anaerobic bacteria can outnumber the lactobacilli, leading to an infection.

You can be more likely to get bacterial vaginosis due to the following: 

  • Sex: Semen has a different pH to your vagina, so contact during sex can sometimes disrupt the natural balance. You’re more likely to get BV if you’re sexually active, you’ve changed sexual partners, or you have multiple sexual partners – although some women who haven’t had sex can still develop it.
  • Hygiene: Having bubble baths and over-cleaning with highly perfumed soaps can alter the pH balance of your vagina as these products are more alkaline.
  • IUD: Also known as the copper coil, this contraceptive can increase anaerobic bacteria in the vagina.
  • Changes in hormone levels: Some women get BV during puberty, pregnancy or the menopause as these hormonal changes can affect the acidity of your vagina.
  • Clothes: Anaerobic bacteria thrive in airless places, so wearing tight-fitting trousers and synthetic underwear can make your vagina the ideal environment for the bacteria to grow.
  • Vaginal douching: This may remove normal vaginal flora, as well as push bacteria up into the uterus, fallopian tubes and ovaries if there is already an infection.

What are the symptoms of bacterial vaginosis?

About half of women with BV won’t have any noticeable symptoms. If you do show signs of bacterial vaginosis, the main symptom will be a change in your vaginal discharge, which may:

  • be a grey-white colour
  • be thin and watery
  • have an unpleasant ‘fishy’ smell
  • have a more noticeable smell after sex
  • be thicker after sex or after your period.

Less commonly, you may have:

  • a burning sensation when you urinate
  • pain during sex
  • vaginal itching.

You should see a doctor if any of these apply to you:

  • Your symptoms don’t improve within 3 days, or they’ve not gone away within 7 days
  • You’ve used an over-the-counter treatment, but your symptoms haven’t gone away
  • You’re pregnant or breastfeeding
  • You have multiple sexual partners or a new sexual partner
  • You have a fever, chills or nausea
  • You have lower tummy pain
  • You have abnormal vaginal bleeding between periods.

How can you diagnose bacterial vaginosis?

Usually you’ll be able to recognise the symptoms yourself, but if you’re not sure, speak to your pharmacist. If treatment hasn’t helped, see your doctor – they may use one of these tests to confirm whether you have BV:

  • PH test: A test strip is placed in your vagina and if the colour change shows that it’s less acidic (a pH of over 4.5) it’s likely to be BV. You can also get this test over the counter
  • Swab test: A sample of your discharge is taken from your vagina to analyse in a lab – this can determine what type of bacteria is present.

Complications of bacterial vaginosis

If untreated, BV can lead to:

  • Pregnancy complications: If you’re pregnant, you have a slightly increased risk of early labour. You can also be more likely to get an infection in your womb after giving birth
  • Pelvic inflammatory disease (PID): BV can sometimes cause PID – an infection in your uterus and fallopian tubes that can lead to infertility
  • In-vitro fertilization (IVF) problems: IVF may be less likely to succeed if you have BV
  • Sexually transmitted infections (STIs): Bacterial vaginosis can increase your chances of developing another infection as your defences are lowered.

How is bacterial vaginosis treated?

It can be quite upsetting if you notice changes in your discharge, and it can make you feel unclean, but it’s important that you don’t wash or douche with perfumed soaps.

BV is very treatable. If it’s milder, and you follow the self-care advice below, it may clear up on its own. But if the symptoms are more obvious you should get treatment. It’s also important to get treatment if you’re pregnant to avoid complications.

Treatment for bacterial vaginosis

If you know you have BV, you don’t always need to have an examination or a test – you can buy effective medicines over the counter or on prescription:

  • Tablets: You can take a course of antibiotics. Metronidazole is the most common and is recommended for pregnant women. Tinidazole can be also be taken if you know you’re intolerant to metronidazole, but pregnant women shouldn’t take this.
  • Topical treatment: You can also use pessaries – creams and gels that you insert in your vagina with an applicator. These include metronidazole gel and clindamycin cream.

Creams and tablets work just as well as each other – speak to your pharmacist or doctor if you’re not sure what’s best for you.

It’s important to note that creams can damage condoms and diaphragms.

If your treatment doesn’t work

If you still have symptoms a week after starting treatment, see your doctor. It may be that:

  • you haven’t used your treatment correctly
  • you’ve had another bout of thrush in close succession
  • you have something other than bacterial vaginosis, such as thrush or an STI.

Self-care for bacterial vaginosis

There are a few things you can do to relieve your symptoms, as well as prevent another episode of BV:

  • Wash your vulva with water and an unscented, mild cleanser – don't wash inside your vagina or use a vaginal douche
  • Use an emollient on your vulva to moisturise and protect the skin
  • Wear loose-fitting, cotton underwear and trousers 
  • When washing your underwear, use non-bio detergent and avoid fabric conditioners
  • Use unscented pads instead of tampons, and change them frequently
  • Use a condom during sex
  • Clean sex toys after every use
  • If you’re on antibiotics, try to replenish the good bacteria by eating plain yoghurt, fermented foods and probiotic supplements.

Related conditions

You shouldn’t assume that vaginal discharge alone means you have bacterial vaginosis as there are similar conditions:

  • Thrush: If your discharge is thick and odourless, and your vulva is itchy and sore, it’s more likely to be thrush
  • Sexually Transmitted Infections (STIs): Similar to bacterial vaginosis, STIs like chlamydia and gonorrhoea can cause an unusual vaginal discharge, so if you’re not sure it’s BV and you’ve recently changed sexually partners or you have multiple partners, take an STI test.

Reviewed by: Dr Unnati Desai