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 infections in women of reproductive age and one of the most misunderstood. While it is not considered a sexually transmitted disease (STD), BV is associated with the same risk factors as chlamydia, gonorrhea, and trichomoniasis. Even women who don't have sex can get BV, albeit uncommonly.

The simple truth is that scientists are not entirely sure which mechanisms (or combination of mechanisms) give rise to BV.

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 potential triggers include sexual practices, genetics, and general/vaginal health.

Sexual Causes

Bacterial vaginosis is not considered an STD because the infection is not caused by a foreign pathogen such as a virus (like HIV) or a bacteria (like syphilis). Instead, the 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).

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.

Among the key sexual risk factors:

  • 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 percent.
  • 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 risk.

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).

If only aerobic bacteria are involved, the infection would be referred to as aerobic vaginitis (AV). Clinically speaking, BV and AV infections are usually hard to tell apart and will require lab testing to differentiate.


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

While the current research is nowhere near conclusive, there is evidence that certain genetic mutations may affect the production of corticotropin-releasing hormone (CRH), a substance which 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 African American women are twice as likely to get BV than their white counterparts.

General/Vaginal Health

Maintaining the optimal vaginal 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 health practices or conditions most associated with 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.
  • 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.
  • Vitamin D deficiency has long been debated as a cause of BV, with some studies supporting the theory and others not. Where it does seem to have a direct impact is during pregnancy. This is evidenced in part by a 2015 study which showed that a 2,000 IU supplement of vitamin D taken daily for 15 weeks reduced the risk of BV from 63.5 percent to 19.2 percent.

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


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.

U.S. Department of Health and Human Services. "Douching." Rockville Maryland; updated April 18, 2017.