Bacterial vaginosis (BV) is not classified as a sexually transmitted infection. It develops when the natural balance of bacteria in the vagina shifts, not because a specific pathogen is passed from one person to another. That said, sexual activity is one of the strongest risk factors for developing BV, and the line between “sexually associated” and “sexually transmitted” has gotten blurrier as research evolves.
Why BV Isn’t Classified as an STI
Traditional STIs like chlamydia or gonorrhea are caused by a specific organism that passes between partners during sex. BV works differently. A healthy vagina is dominated by protective bacteria called lactobacilli, which keep the environment slightly acidic and inhospitable to harmful microbes. BV happens when those lactobacilli lose their foothold and a mix of other bacteria, particularly anaerobes, overgrow and form a complex community. There’s no single “BV germ” being transmitted.
This is why BV can occur in people who have never had sex. Anything that disrupts the vaginal microbiome, such as douching, scented hygiene products, or even hormonal changes, can trigger it. The vagina naturally hosts around 50 different microbial species, and when that ecosystem tips out of balance, BV is the result.
The Sexual Activity Connection
Even though BV isn’t an STI by definition, sex clearly plays a role. New sexual partners, multiple partners, and unprotected sex all raise the risk. Among women who have sex with women, BV rates are notably high, and partners often share the same BV-associated bacteria, suggesting the condition can be passed between female partners.
In a significant shift, the American College of Obstetricians and Gynecologists issued new guidance in 2025 recommending that male sexual partners of women with recurrent BV be treated with antibiotics at the same time. Previously, there wasn’t enough evidence to support this. The updated recommendation reflects growing data that BV-associated bacteria can live in the male genital tract and get reintroduced during sex, fueling the cycle of recurrence. This is perhaps the strongest signal yet that BV behaves, at least partly, like a sexually transmitted condition, even if it isn’t formally labeled one.
What BV Looks and Feels Like
Many people with BV have no symptoms at all. When symptoms do appear, the most recognizable is a thin, grayish-white discharge with a fishy smell that often gets stronger after sex. The discharge tends to be milklike and smooth rather than chunky (which would point more toward a yeast infection). Vaginal pH rises above 4.5, meaning the environment becomes less acidic than normal.
Doctors diagnose BV by checking for at least three of four clinical signs: the characteristic discharge, a pH above 4.5, the fishy odor, and the presence of “clue cells” (vaginal cells coated in bacteria) under a microscope. It’s a straightforward office test, and results are typically available the same day.
BV Raises Your Risk of Actual STIs
One of the most important reasons to treat BV, even if it isn’t an STI itself, is that it makes you significantly more vulnerable to infections that are. The disrupted bacterial environment and inflammation that come with BV weaken the vaginal lining’s natural defenses.
The numbers are striking. BV is associated with a 60% increased risk of acquiring HIV. In a large study of African couples, men whose female partners had BV were more than three times as likely to contract HIV compared to men whose partners had normal vaginal flora, even after accounting for other risk factors like condom use, circumcision, and viral load. BV also increases susceptibility to chlamydia and gonorrhea.
Treatment and the Recurrence Problem
BV sometimes resolves on its own, but antibiotics are the standard treatment. Most people feel better within a few days of starting treatment, and the course is typically short. The bigger challenge is keeping BV from coming back. Between 50% and 80% of women experience a recurrence within 6 to 12 months of finishing antibiotics. That recurrence rate is one of the highest of any common vaginal condition.
This is where the partner treatment recommendation matters. If BV-associated bacteria are living in a male partner’s genital tract, antibiotics for one partner alone may not break the cycle. Treating both partners simultaneously appears to reduce the odds of recurrence, at least in heterosexual couples. Research on the best approach for same-sex partners and people in nonmonogamous relationships is still catching up.
What Increases Your Risk
Beyond sexual activity, several habits and circumstances shift the odds:
- Douching strips away protective lactobacilli and disrupts vaginal pH. When the body tries to replenish those bacteria, it can overshoot and trigger an imbalance. There is no medical reason to douche.
- Scented products like feminine sprays, powders, wipes, and scented body wash can irritate vaginal tissue and disrupt the microbiome. Warm water and a gentle, unscented soap are sufficient.
- New or multiple sexual partners introduce unfamiliar bacteria that can destabilize the existing microbial community.
- Smoking has been consistently linked to higher BV rates, likely through effects on immune function and vaginal chemistry.
The Bottom Line on Classification
BV sits in a gray zone. It’s not caused by a single sexually transmitted organism, so it doesn’t meet the traditional definition of an STI. But sexual activity is deeply intertwined with how it develops, recurs, and spreads, particularly between female partners. The medical community’s growing willingness to treat sexual partners reflects a quiet acknowledgment that the old binary of “STI or not” doesn’t fully capture what BV is. For practical purposes, if you’re dealing with recurrent BV, treating it as though sexual transmission plays a role is now part of mainstream medical advice.