Causes and Risk Factors of Bacterial Vaginosis

How Sexual and Health Practices Contribute to Risk

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Bacterial vaginosis (BV) is the most common vaginal infection in women of reproductive age and one of the most misunderstood. BV is associated with the same risk factors as chlamydia, gonorrhea, and trichomoniasis. In fact, scientists aren't even entirely sure which mechanisms give rise to BV or why some women are prone to the infection and others aren't.

What we do know is that, whatever the underlying cause, BV is the result of an imbalance in the vaginal flora in which healthy bacteria are depleted, allowing unhealthy ones to proliferate. Some of the possible triggers include sexual practices, genetics, and general/vaginal health.

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Common Causes

BV infection occurs when certain "bad" bacteria commonly found in the vagina are given the opportunity to thrive.

The culprits include Gardnerella vaginalis, Atopobium vaginae, and strains of the Prevotella and Morbiluncus bacteria. These bacteria are usually kept in check by the immune system and, more importantly perhaps, the acidity of the vagina (as measured by the vaginal pH).

It is not clear whether BV should be considered an STD, but some believe that Gardnerella can be transmitted from one partner to another.

The very act of sexual intercourse can undermine these systems by introducing new microbes into the vaginal flora. This may not only alter the vaginal pH, it can strip away many of the healthy bacteria that support and "clean" the vagina. As such, the more sexual partners you have, the more you expose yourself to their microbes.

The risk of BV, not surprisingly, is highest among women aged 15 and 44 who are more likely to be sexually active. It is rare that a woman who has never been sexually active has bacterial vaginosis.

In addition to BV, women can develop what is called a mixed infection as a result of a sexual contact. Mixed infection occurs when the vagina is inoculated with anaerobic bacteria commonly found in the vagina as well as aerobic bacteria foreign to the vagina. Examples of aerobic bacteria include Staphylococcus aureus and Escherichia coli (E. coli).


In some cases, a woman's genetics may contribute to her BV risk, usually by causing lower-than-expected levels of protective lactobacilli in the vagina.

While the research is nowhere near conclusive, there is evidence that certain genetic mutations may affect the production of corticotropin-releasing hormone (CRH), a substance that plays an important role in regulating immunity and inflammation. Scientists believe that abnormalities in CRH production may affect vaginal tissues and trigger an imbalance in bacteria populations, especially during pregnancy.

A number of CRH-related genetic mutations have been identified in black women that are less common in white women. This may help explain, in part, why black women are twice as likely to get BV than their white counterparts.

Lifestyle Risk Factors

Sexual practices, vaginal health, and general health all play a part in establishing your personal risk of bacterial vaginosis. All of these factors are modifiable, meaning that you can change them and reduce your risk of infection:

Sexual Risk Factors

While bacterial vaginosis is not a sexually transmitted disease, it shares many of the same characteristics in that it is promoted by certain sexual activities. Key among these:

  • Multiple sex partners is one of the major risk factors of BV. This includes both male and female partners. In fact, a 2010 study concluded that having sex with another woman increases your risk of BV by as much as 52%.
  • New sex partners pose a risk simply by introducing you to bacteria and other microorganisms your body may not be unaccustomed to.
  • Unprotected oral, vaginal, and anal sex contribute by removing the barrier of protection that condoms and dental dams provide. BV can also be caused by manual sex (masturbation, "fingering") and frottage ("dry humping").
  • Shared sex toys also pose a potential risk.

In term of vaginal health, maintaining the optimal pH and flora is not always easy. Many of the everyday practices we engage in can undermine this delicate balance, either by promoting the overgrowth of "bad" bacteria or impairing our ability to fight infection.

Among the practices or conditions most associated with a BV infection:

  • Douching places you at risk by stripping the vagina of its protective flora. According to a report from the U.S. Department of Health and Human Services, one in five American women aged 15 to 44 douche. The practice is most common among teens, African-American women, and Latino women.
  • Smoking is known to deplete two bacteria vital to your vaginal health: Lactobacillus iners and Lactobacillus crispatus. Smoking also causes the constriction of blood vessels, making it harder to fight infection when increased circulation is needed.
  • Copper-containing intrauterine devices (IUDs), while effective in preventing pregnancy, can double the risk of BV in certain women. According to a study from the St. Louis School of Medicine, the risk appears greatest in women who have an underlying imbalance in their vaginal flora (often undiagnosed) and experience irregular bleeding while using an IUD.

By better understanding the risks of bacterial vaginosis, you can find the means to prevent it and avoid other, more serious sexually transmitted infections.

Frequently Asked Questions

  • What causes bacterial vaginosis?

    Bacterial vaginosis (BV) is caused by an imbalance in the vaginal flora that allows unhealthy bacteria to proliferate. While scientists haven't pinpointed an exact cause, BV can be the result of several different potential risk factors, such as douching, smoking, having an intrauterine device, and having multiple sex partners. Genetics also play a big role.

  • Is BV a sexually transmitted disease?

    No, BV is not considered a sexually transmitted disease (STD), because it is not technically caused by a pathogen such as a virus or bacteria. BV simply develops when "bad" bacteria that are often found in the vagina overgrow and throw off the delicate flora balance.

  • Does BV only affect women?

    BV infections only affect women or people with vaginas. However, men or people with penises can transmit the bacteria, even though it won't lead to infection in themselves.

  • Why might bacterial vaginosis keep coming back?

    Unlike some infections, having BV once doesn't mean you can't get it again. In some cases, it can be a chronic condition. If you have symptoms, it's a good idea to seek treatment and take the full course of antibiotics to clear the infection, and then talk to your healthcare provider about investigating the root cause.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • Brotman, R.; He, X.; Gajer, P. et al. Association between cigarette smoking and the vaginal microbiota: a pilot study.BMC Infect Dis. 2014; 14:471. DOI: 10.1186/1471-2334-14-471.

  • Madden, T.; Grentzer, J.; Secura, G. et al. Risk of Bacterial Vaginosis in Users of the Intrauterine Device: A Longitudinal Study.Sex Trans Dis. 2012; 39(3):217-22. DOI: 10.1097/OLQ.0b013e31823e68fe.

  • Ryckman, K.; Simhan, H.; Krohn, A. et al. Predicting risk of bacterial vaginosis: the role of race, smoking and corticotropin-releasing hormone-related genes.Mol Hum Reproduction. 2009; 15(2):131-137. DOI: 10.1093/molehr/gan081.

  • Taheri, M.; Baheiraei, A.; Foroushani, A. et al. Treatment of vitamin D deficiency is an effective method in the elimination of asymptomatic bacterial vaginosis: A placebo-controlled randomized clinical trial.Indian J Med Res. 2015; 141(6):799-806. DOI: 10.4103/0971-5916.160707.

  • Turner, A.; Carr Reese, P.; and Fields, K. A blinded, randomized controlled trial of high-dose vitamin D supplementation to reduce recurrence of bacterial vaginosis.Am J Obstet Gynecol. 2014;211(5):479.e1-479.e13. DOI: 10.1016/j.ajog.2014.06.023.