Bacterial vaginosis is not classified as a sexually transmitted infection, but the relationship between BV and sex is complicated. BV is the most common vaginal condition in women of reproductive age, and it rarely occurs in people who have never been sexually active. That paradox is exactly why this question comes up so often: BV behaves like an STI in some ways but doesn’t fit neatly into that category.
Why BV Isn’t Classified as an STI
A sexually transmitted infection is caused by a specific pathogen passed between partners during sex, like chlamydia or gonorrhea. BV doesn’t work that way. It’s a disruption of the vaginal microbiome, where the protective bacteria that normally dominate the vagina get replaced by an overgrowth of anaerobic bacteria. The CDC classifies it as a “vaginal dysbiosis,” essentially an imbalance rather than an infection caused by one identifiable germ.
Several types of bacteria are involved in BV, and many of them are found in healthy vaginas in smaller numbers. The shift from a balanced environment to an imbalanced one is what causes symptoms. Scientists still don’t fully understand what triggers this shift, and whether a single sexually transmitted pathogen could be responsible remains an open question.
BV can also develop without any sexual contact at all. Douching is a well-documented risk factor, as it disrupts the natural bacterial balance. This is one of the clearest reasons BV doesn’t meet the strict definition of an STI.
The Strong Link to Sexual Activity
Even though BV isn’t an STI, sex is one of its biggest risk factors. People who have never had sex are rarely affected. Having a new sexual partner, multiple partners, or not using condoms all increase the risk. BV can also spread between female sexual partners.
For years, the standard guidance was that treating a sexual partner had no effect on whether BV came back. That thinking has started to shift. In 2025, the American College of Obstetricians and Gynecologists recommended for the first time that in some cases, male sexual partners should be treated alongside the person with recurrent BV. This recommendation followed new research showing that sexual activity plays an important role not just in getting BV, but in getting it again after treatment.
The CDC puts it plainly: researchers know BV occurs most often in sexually active people, but they still don’t know exactly how sex causes it. That gap in understanding is a big part of why the classification remains unsettled.
Symptoms and How It’s Diagnosed
Many people with BV have no symptoms at all. When symptoms do appear, the most common is a thin, grayish-white vaginal discharge with a noticeable fishy odor, often stronger after sex. Some people also experience mild itching or burning during urination.
A healthcare provider can diagnose BV through a vaginal exam. They’ll look at a sample of discharge under a microscope for characteristic “clue cells,” which are vaginal cells coated with bacteria. They may also check the vaginal pH, which tends to be higher than normal (above 4.5) when BV is present. A whiff test, where a chemical is added to the discharge to see if it produces a fishy smell, is another common step.
Treatment and the Problem of Recurrence
BV is treated with antibiotics, typically a course lasting five to seven days. Treatment is effective at clearing symptoms in most cases. The bigger problem is that BV comes back, and it does so frequently. Between 50% and 80% of women experience a recurrence within 6 to 12 months of finishing antibiotic treatment.
That high recurrence rate is one reason the conversation around partner treatment has changed. If bacteria associated with BV can be harbored by a sexual partner and reintroduced during sex, treating only one person may not be enough to break the cycle. The new ACOG guidelines reflect this logic, though partner treatment is currently recommended specifically for recurrent cases rather than every first episode.
Avoiding douching is one of the most practical things you can do to reduce your risk of both initial BV and recurrences. Douching strips away the protective Lactobacillus bacteria that keep the vaginal environment acidic and inhospitable to the anaerobic bacteria behind BV. Condom use is also associated with lower rates of BV.
Why BV Still Matters for Sexual Health
Even though BV itself isn’t an STI, having it raises your risk of acquiring one. BV disrupts the vaginal lining and changes the local immune environment, making it easier for other infections to take hold. One study of African couples found that BV was associated with a roughly threefold increased risk of female-to-male HIV transmission, partly because BV-associated bacteria can increase viral concentrations in vaginal fluids. BV has also been linked to higher susceptibility to other STIs.
During pregnancy, untreated BV is associated with preterm birth and low birth weight. Outside of pregnancy, it can increase the risk of infection after gynecological procedures. These complications make treatment worthwhile even when symptoms seem mild or tolerable.
The Bottom Line on Classification
BV occupies a gray zone. It’s not an STI by the traditional definition because it’s not caused by a single transmissible pathogen and can occur without sexual contact. But sexual activity is its strongest risk factor, it can be passed between female partners, and treating male partners now appears to reduce recurrence. The medical community increasingly recognizes BV as sexually associated, even if it stops short of calling it sexually transmitted. If you’ve been diagnosed with BV, it doesn’t mean you or your partner has been unfaithful, and it doesn’t mean you have an STI. It means the bacterial balance in your vagina has shifted, and sex is one of several factors that can make that happen.