Are you noticing a fishy smell and watery discharge coming from your vagina? This could be a sign of bacterial vaginosis, a common and uncomfortable vaginal condition.

In this story we cover:

  • What exactly is bacterial vaginosis?
  • What causes bacterial vaginosis?
  • How can you get bacterial vaginosis and what are the risk factors?
  • What are the symptoms of bacterial vaginosis?
  • Diagnosis of bacterial vaginosis

1. What Exactly is Bacterial Vaginosis?

Bacterial vaginosis (BV) is a very common genital condition that affects 30% of women of reproductive age1.

It is caused by uncontrollable growth of bad (pathogen) bacteria in or around the vagina. The bacteria that cause BV are often present in a healthy vagina too, but when the balance of good bacteria is disrupted, it can lead to an overgrowth of bad bacteria. We go into more detail about what the bacteria organisms cause BV below.

So why can the bad bacteria sometimes be present without BV occurring? Because the good bacteria also present in the vagina are keeping them at bay and under control. But once your vagina’s good bugs or beneficial microbiome is weakened, disrupted, or eradicated, balance is lost, creating an opportunity for pathogen bacteria to overgrow.

BV can be triggered by several factors, including changes in the pH level of the vagina. Good bacteria in the vagina produce lactic acid, which creates an acidic environment with a pH between 3.8-4.5. This environment makes it difficult for bad bacteria to survive. However, if the pH level of the vagina increases above 4.5, it can stimulate the growth of bad bacteria, leading to BV.

2. What Causes Bacterial Vaginosis?

The most common causes of bacterial vaginosis are tiny bacteria that grow well in an environment without oxygen. Three examples of the most bacteria which cause BV are:

  • Gardnerella vaginalis – this bacteria is often present in a healthy vaginal microbiome but its overgrowth is a sign that the healthy vaginal microbiome balance has been disrupted.
  • Atopobium vaginae  the second most important suspect contributing toward BV development. Like G. vaginalis, it can be found in a healthy vagina (8-25%), but it is much more common in BV patients (50-96%).
  • Prevotella biviaP. bivia tends to grow quickly when the levels of good bacteria in the vagina are disturbed, appearing in higher numbers just prior to BV incidents. Therefore P. bivia is recognised as a BV trigger, enhancing the growth of G. vaginalis and other bad bugs associated with BV2.

If you develop an infection such as bacterial vaginosis, just remember it is common and may happen even if you take good care of your health and keep all the lifestyle precautions possible.

3. How can you get bacterial vaginosis and what are the risk factors?

When the healthy bacteria in your vagina are thrown off balance – disturbing your vaginal microbiome – pathogen or bad bacteria such as Gardnerella vaginalis can take over and grow very quickly, causing a bacterial vaginosis.

What can upset the balance of healthy bacteria in the vagina? Certain actions or habits can cause irritation and throw off the balance of good bacteria in the vagina. Examples include:

  • Use of antibiotics
  • Use of spermicides
  • Use of tampons
  • Douching (washing out your vagina)
  • Sexual intercourse3
  • Changes in hormonal levels (due to pregnancy, breastfeeding, menopause or birth control pills)
  • A diet high in fat and with a low intake of fruits and vegetables (specifically low levels of vitamin A, folate and calcium)4
  • Ethnic background – For example, African American women have around 50% higher risk of BV5, which is in relation to their vaginal microbiome composition6
  • Sexual behaviours  A study done on more than a thousand sexually active young Australian women (aged 16-25) found that prevalence of BV and abnormal vaginal microbiome was increased in participants who had a recent female partner or more than 5 male partners within a year7. While sexual activity was directly associated with the development of BV, even women who are not yet sexually active5 can develop BV.

4. What are the symptoms of bacterial vaginosis?

The most common symptoms of bacterial vaginosis are:

  • an unpleasant odour (described as fishy smell)
  • vaginal discharge (can be grey colour, or abnormal volume and consistency)
  • soreness
  • itching, irritation
  • burning pain

Please note, you may have some of these symptoms (e.g., itching or discharge) without having an infection.

On the other hand, you can have bacterial vaginosis but not experiencing any symptoms. Up to 50% of women with bacterial vaginosis are asymptomatic8. One study showed that 84% of participants reported no symptoms despite being found to have BV5.

5. Diagnosis of bacterial vaginal infection

Bacterial vaginosis is diagnosed by your GP. Depending on symptoms and clinical history your physician can do testing such as the following:

  • Pelvic examination  physical examination of your organs in pelvic area, where a health practitioner will insert one or two fingers (gloved and lubricated) of one hand in your vagina or rectum and gently press the lower abdomen with other hand. The procedure although not comfortable should not be painful.
  • Saline wet mount  vaginal discharge looked through a microscope. The test is positive for BV if “clue cells” (vaginal wall cell heavily covered with bacteria cells) are found.
  • Whiff test (odour test)  vaginal discharge sample is mixed with 10% KOH (potassium hydroxide) solution and then “sniffed”. Fishy odour is developed in positive BV samples.
  • pH testing  pH higher than 4.5 is a signal for concern, BV usually shows pH value around 5-6
  • Nugent score  microscopic analysis of vaginal swab sample which has been grain stained. The number of different bacteria species can be used to calculate a Nugent score (a scoring system use to diagnose bacterial vaginosis). Score 0-3 is negative for BV, score 4-6 has been considered intermediate, while score >7 indicates that a sample is BV positive. 
  • qPCR (quantitative PCR) - molecular biology technique that examines the presence and quantity of good and bad bugs within a vaginal swab sample
  • Bacterial culture  bugs are isolated and identified from a vaginal swab sample which is cultivated using different growth mediums. 

It is important, for the any of the above sample tests to be accurate, not to have sex, not to use spermicides and not to douche for at least 3 days before your visit to a physician/GP if you are concerned you have bacterial vaginosis.

6. Treatment for bacterial vaginal infection

The treatment your GP or doctor may prescribe include use of products that will be applied orally or vaginally. It is important to seek diagnosis from your healthcare professional before treatment so you can be sure that your infection is bacterial vaginosis.

It is important to follow the treatment instructions untill completion, even if symptoms cease, as an infection causing bacteria may still be present, and it could reoccur if treatment is not followed properly or completed fully.

Antibiotic treatment for BV

The following are common antibiotic treatments for BV[8] that your GP may prescribe.

  • Metronidazole – orally, 500 mg, twice daily, for 7 days
  • Metronidazole – vaginal cream 0.75%, twice daily, for 5 days
  • Clindamycin – vaginal cream 2%, once daily, for 7 days

Rebalancing the Vaginal Microbiome using Probiotics

Vaginal probiotics were studied in 10 clinical trials (blind, controlled and randomized) involving over 2300 patients with BV. The collective results of these 10 trials showed that probiotics are safe and can improve symptoms and restore a healthy vaginal microbiome with both short- and long-term treatment9. The positive long-term effect of the vaginal probiotics was much greater when compared with the placebo, in restoring a healthy vaginal microbiome, when followed up after 2 months of treatment.

7. Why do I keep getting bacterial Vaginosis?

If your infection reoccurs, you are not alone. In fact, BV recurrence in the first year after antibiotic treatment can be as high as 58%10. The research showed that this was possibly due to the bacterial resistance to antibiotics and reintroduction of BV bacteria through sexual intercourse11.

8. Prevention of vaginal bacterial infection

Maintaining healthy vaginal microflora and avoiding irritant products and practises are the best way to support and nurture your vaginal health. In a nutshell:

  • Use of vaginal probiotics12 vaginal probiotics contain good bugs that can colonize and provide a beneficial effect in the vaginal environment. Once established in vagina, good bugs from the probiotics will produce lactic acid and lower vaginal pH levels, which in turn helps to suppress bad bacteria growth. Probiotics can also create substances that can help to break down the protective layer harmful bacteria make (known as biofilm), preventing the bad bacteria from attaching to the vaginal wall, while also strengthening the body's immune system.
  • Choose good quality washes, lubricants and hygiene products which will not alter vaginal pH and disturb vaginal microbiome
  • Avoid douches – douching once or more per month is a risk factor for BV13
  • Carefully clean any contraceptive device (diaphragms, cervical caps, and spermicide applicators) before and after each use
  • Use condoms during sex
  • Carefully clean any feminine hygiene products such as menstrual cups before and after each use
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See list of references used on this page

1 Allsworth JE, Peipert JF. Prevalence of bacterial vaginosis:2001-2004 National Health and Nutrition Examination Survey data. Obstet Gynecol. 2007 Jan;109(1):114-20.

2 Randis TM, Ratner AJ. Gardnerella and Prevotella: Co-conspirators in the Pathogenesis of Bacterial Vaginosis. J Infect Dis. 2019 Aug 30;220(7):1085-1088. 

3 Fethers KA, Fairley CK, Hocking JS, Gurrin LC, Bradshaw CS. Sexual risk factors and bacterial vaginosis: a systematic review and meta-analysis. Clin Infect Dis. 2008 Dec 1;47(11):1426-35. 

4 Neggers YH, Nansel TR, Andrews WW, Schwebke JR, Yu KF, Goldenberg RL, Klebanoff MA. Dietary intake of selected nutrients affects bacterial vaginosis in women. JNutr. 2007 Sep;137(9):2128-33.

5 Koumans EH, Sternberg M, Bruce C, McQuillan G, Kendrick J, Sutton M, Markowitz LE. The prevalence of bacterial vaginosis in the United States, 2001-2004; associations with symptoms, sexual behaviors, and reproductive health. Sex Transm Dis. 2007 Nov;34(11):864-9. 

6 Fettweis JM, Brooks JP, Serrano MG, Sheth NU, Girerd PH, Edwards DJ, Strauss JF, The Vaginal Microbiome Consortium, Jefferson KK, Buck GA. Differences in vaginal microbiome in African American women versus women of European ancestry. Microbiology (Reading). 2014 Oct;160(Pt 10):2272-2282.

7 Bradshaw CS, Walker J, Fairley CK, Chen MY, Tabrizi SN, Donovan B, Kaldor JM, McNamee K, Urban E, Walker S, Currie M, Birden H, Bowden F, Garland S, Pirotta M, Gurrin L, Hocking JS. Prevalent and incident bacterial vaginosis are associated with sexual and contraceptive behaviours in young Australian women. PLoS One. 2013;8(3):e57688.

8 Hetal B Gor. “Vaginitis”., Jul 09, 2021.

9 Wang Z, He Y, Zheng Y. Probiotics for the Treatment of Bacterial Vaginosis: A Meta-Analysis. Int J Environ Res Public Health. 2019 Oct 12;16(20):3859. 

10 Bradshaw CS, Morton AN, Hocking J, Garland SM, Morris MB, Moss LM, Horvath LB, Kuzevska I, Fairley CK. High recurrence rates of bacterial vaginosis over the course of 12 months after oral metronidazole therapy and factors associated with recurrence. J Infect Dis. 2006 Jun 1;193(11):1478-86.

11 Bradshaw CS, Sobel JD. Current Treatment of Bacterial Vaginosis-Limitations and Need for Innovation. J Infect Dis. 2016 Aug 15;214 Suppl 1(Suppl 1):S14-20.

12 Rönnqvist PD, Forsgren-Brusk UB, Grahn-Håkansson EE. Lactobacilli in the female genital tract in relation to other genital microbes and vaginal pH. ActaObstetGynecolScand. 2006;85(6):726-35.

13 Ness RB, Hillier SL, Richter HE, Soper DE, Stamm C, McGregor J, Bass DC, Sweet RL, Rice P. Douching in relation to bacterial vaginosis, lactobacilli, and facultative bacteria in the vagina. ObstetGynecol. 2002 Oct;100(4):765.