Bacterial vaginosis - vaginal microbiota imbalance

The most common gynecological disorder in women of childbearing age, bacterial vaginosis affects 23%-29% of women worldwide.1 The disorder is hit and miss: it can go completely unnoticed or significantly alter a woman’s life. The cause remains unknown, but a vaginal microbiota imbalance seems the most likely explanation.2

Created 02 August 2021
Updated 30 May 2024
Is bacterial vaginosis a disease?

About this article

Created 02 August 2021
Updated 30 May 2024

What is bacterial vaginosis?

Bacterial vaginosis is a harmful and hard to detect disorder. 50% of women are asymptomatic, while others suffer from local irritation or foul-smelling discharge.3

In practice, doctors use the Amsel score4 to diagnose bacterial vaginosis. Diagnosis is based on the presence of at least three of the following criteria:

  • Thin, homogeneous vaginal discharge 
  • A vaginal pH above 4.5 
  • An amine smell (similar to a fishy smell) after a specific test is performed on a vaginal smear
  • Presence of vaginal tissue cells coated with bacteria when discharge is examined microscopically

Many risk factors are associated with the disease, including age, menstrual cycle, pregnancy, and sexual history, but also vaginal douching and smoking.3 A vaginal dysbiosis induced by antibiotic treatment may also participate in the development of bacterial vaginosis, creating a vicious circle, since antibiotics can be used to treat the infection.3

Lastly, women with bacterial vaginosis are more likely to contract sexually transmitted infections (STIs), including herpes, HPV, AIDS and bacterial infections.5,6

50% of women are asymptomatic, while others suffer from local irritation or foul-smelling discharge

Is there a link with the vaginal microbiota?

Bacterial vaginosis is associated with an imbalance ( (sidenote: Dysbiosis Generally defined as an alteration in the composition and function of the microbiota caused by a combination of environmental and individual-specific factors. Levy M, Kolodziejczyk AA, Thaiss CA, et al. Dysbiosis and the immune system. Nat Rev Immunol. 2017;17(4):219-232.   ) ) of the vaginal microbiota.2 The vaginal microbiota is dominated by different species of the bacterial genus (sidenote: Lactobacilli Rod-shaped bacteria whose main characteristic is the production of lactic acid, from where they get the name “lactic acid bacteria”.  Lactobacilli are present in the oral, vaginal and gut microbiota of humans, but also in plants and animals. They are found in fermented foods, such as dairy products (e.g. certain cheeses and yoghurts), pickles, sauerkraut, etc. Lactobacilli are also found in probiotics, with certain species recognized for their beneficial properties.   W. H. Holzapfel et B. J. Wood, The Genera of Lactic Acid Bacteria, 2, Springer-Verlag, 1st ed. 1995 (2012), 411 p. « The genus Lactobacillus par W. P. Hammes, R. F. Vogel Tannock GW. A special fondness for lactobacilli. Appl Environ Microbiol. 2004 Jun;70(6):3189-94. Smith TJ, Rigassio-Radler D, Denmark R, et al. Effect of Lactobacillus rhamnosus LGG® and Bifidobacterium animalis ssp. lactis BB-12® on health-related quality of life in college students affected by upper respiratory infections. Br J Nutr. 2013 Jun;109(11):1999-2007. ) . These bacteria help maintain an acidic pH in the vagina and thus prevent the proliferation of pathogenic bacteria.7 The vaginal microbiota also contains yeasts such as Candida albicans in smaller quantities.8

With bacterial vaginosis, this normal microbial flora is replaced by a polymicrobial flora comprising numerous bacteria (Gardnerella, Atopobium, Prevotella, Mobiluncus, etc.).2 This leads to an increase in the pH of the vagina (which is normally very acidic), mainly attributed to the decrease in the predominance of Lactobacillus species.9 However, the mere presence of species from this polymicrobial flora does not in itself seem to cause infection, i.e. a woman whose vagina contains Atopobium or Prevotella species will not necessarily report symptoms. In fact, Gardnerella vaginalis is present in 90% of symptomatic subjects and 45% of healthy subjects.4 For a long time, this bacterium was considered the main pathogen behind bacterial vaginosis, but new research has shown that Gardnerella vaginalis can colonize the vagina without triggering infection.10 The causes of the infection are yet to be determined and research in the area continues.3

35% Only 1 in 3 women know that bacterial vaginosis is associated with an imbalance in the vaginal microbiota

How to avoid bacterial vaginosis

Treatment is only recommended for women who are symptomatic. Recommended treatment currently involves the prescription of oral or vaginal antibiotics.2 While antibiotics may help alleviate symptoms, relapse is unfortunately very common.11

However, there are a number of ways to reduce your chances of getting bacterial vaginosis. Firstly, avoid certain risk factors, such as vaginal douching or smoking.3 Vaginal or oral probiotics,12,13 that restore the balance of the vaginal microbiota can be used to treat or prevent relapses.

This article is based on scientifically approved sources. If you experience symptoms, please consult your family doctor or gynecologist.


1  Peebles K, Velloza J, Balkus JE, et al. High Global Burden and Costs of Bacterial Vaginosis: A Systematic Review and Meta-Analysis. Sex Transm Dis. 2019 May;46(5):304-311. 

2 Chen X, Lu Y, Chen T, et al. The Female Vaginal Microbiome in Health and Bacterial Vaginosis. Front Cell Infect Microbiol. 2021 Apr 7;11:631972. 

3 Coudray MS, Madhivanan P. Bacterial vaginosis-A brief synopsis of the literature. Eur J Obstet Gynecol Reprod Biol. 2019 Dec 24;245:143-148

4 Onderdonk AB, Delaney ML, Fichorova RN. The Human Microbiome during Bacterial Vaginosis. Clin Microbiol Rev. 2016 Apr;29(2):223-38. 

5 Lewis FM, Bernstein KT, Aral SO. Vaginal Microbiome and Its Relationship to Behavior, Sexual Health, and Sexually Transmitted Diseases. Obstet Gynecol. 2017;129(4):643-654.

6 Torcia MG. Interplay among Vaginal Microbiome, Immune Response and Sexually Transmitted Viral Infections. Int J Mol Sci. 2019;20(2):266.

7 Greenbaum S, Greenbaum G, Moran-Gilad J, et al. Ecological dynamics of the vaginal microbiome in relation to health and disease. Am J Obstet Gynecol. 2019 Apr;220(4):324-335.

8 d'Enfert C, Kaune AK, Alaban LR, et al. The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives. FEMS Microbiol Rev. 2020 Nov 24:fuaa060. 

9 Aldunate M, Srbinovski D, Hearps AC, et al. Antimicrobial and immune modulatory effects of lactic acid and short chain fatty acids produced by vaginal microbiota associated with eubiosis and bacterial vaginosis. Front Physiol. 2015 Jun 2;6:164. 

10 Muzny CA, Taylor CM, Swords WE, et al. An Updated Conceptual Model on the Pathogenesis of Bacterial Vaginosis. J Infect Dis. 2019 Sep 26;220(9):1399-1405. 

11 Bradshaw CS, Brotman RM. Making inroads into improving treatment of bacterial vaginosis - striving for long-term cure. BMC Infect Dis. 2015 Jul 29;15:292. 

12 López-Moreno A, Aguilera M. Vaginal Probiotics for Reproductive Health and Related Dysbiosis: Systematic Review and Meta-Analysis. J Clin Med. 2021 Apr 2;10(7):1461. 

13 Koirala R, Gargari G, Arioli S, et al. Effect of oral consumption of capsules containing Lactobacillus paracasei LPC-S01 on the vaginal microbiota of healthy adult women: a randomized, placebo-controlled, double-blind crossover study. FEMS Microbiol Ecol. 2020 Jun 1;96(6):fiaa084.