Bacterial vaginosis is not only sexually transmitted. While sexual activity is one of the strongest risk factors for developing BV, it also occurs in people who have never had sex. About 18.8% of women who have never been sexually active are diagnosed with BV, which rules out any classification as a purely sexually transmitted infection.
Why BV Isn’t Classified as an STI
BV happens when the balance of bacteria inside the vagina shifts. Normally, beneficial bacteria keep the vaginal environment slightly acidic, which prevents harmful bacteria from multiplying. When that balance tips, other bacteria overgrow and cause symptoms like a thin, milklike discharge, a fishy odor, or irritation.
Because this imbalance can happen without any sexual contact at all, major health organizations do not classify BV as a sexually transmitted infection in the traditional sense. It’s not caused by a single pathogen that passes from one person to another the way chlamydia or gonorrhea does. Instead, it’s a shift in an entire microbial ecosystem, and many different triggers can set that shift in motion.
How Sexual Activity Increases Risk
That said, sex is clearly involved for many people. The numbers tell a striking story: BV prevalence rises steadily with more sexual partners. Among women with one lifetime partner, the rate is about 22.4%. For those with two to three partners, it climbs to 43.4%, and for those with four or more, it reaches 58%. Something about sexual activity pushes the vaginal environment toward imbalance.
Semen is one likely contributor. It’s alkaline, meaning it temporarily raises vaginal pH. The vagina’s natural acidity is part of its defense system, so repeated exposure to semen can create conditions where harmful bacteria thrive. Lubricants can have a similar effect. Using condoms reduces this exposure and may lower your risk.
There’s also growing evidence that bacteria can be exchanged between partners during sex. In 2025, the American College of Obstetricians and Gynecologists recommended for the first time that male sexual partners of women with recurrent BV be treated with antibiotics alongside their partner. Previously, data hadn’t shown a clear benefit to treating partners, but newer research changed that picture. The fact that treating a male partner can reduce a woman’s recurrence strongly suggests bacteria are being passed back and forth during sex, even if BV itself isn’t a traditional STI.
Non-Sexual Triggers
Several things that have nothing to do with sex can also disrupt vaginal bacteria and lead to BV. Douching is one of the best-documented triggers. It washes away the protective bacteria that maintain acidity, creating an opening for harmful bacteria to take over. Studies have found that women who stop douching are less likely to develop BV.
Scented soaps, body washes, and feminine hygiene products applied inside or near the vagina can cause similar disruption. The vagina is self-cleaning; externally washing the vulva with warm water and a mild soap is all that’s needed. Antibiotics taken for other infections can also wipe out beneficial vaginal bacteria as a side effect, sometimes triggering BV.
Other factors include hormonal changes (during menstruation, pregnancy, or menopause), smoking, and even stress, all of which can alter the vaginal environment enough to allow an overgrowth of the wrong bacteria.
Why It Keeps Coming Back
BV is notoriously recurrent. Many people find it returns within a few months of treatment. This happens partly because antibiotics kill the overgrown bacteria but don’t always restore the beneficial ones. If the protective bacteria don’t bounce back quickly, the same imbalance can develop again.
For people in sexual relationships, reinfection from a partner may also play a role. This is why the new recommendation to treat male partners is significant. If BV-associated bacteria are living on a partner’s skin or in their genital tract, successful treatment of one person can be undone by the next sexual encounter. Concurrent partner treatment aims to break that cycle.
What BV Feels Like
Some people with BV have no symptoms at all. When symptoms do appear, the most common is a thin, grayish-white discharge with a distinct fishy smell that often becomes stronger after sex. You might also notice itching or burning around the vagina, though these are less common than with yeast infections.
BV is diagnosed based on a combination of signs: the characteristic discharge, a vaginal pH above 4.5 (more alkaline than normal), the presence of certain bacterial patterns visible under a microscope, and the fishy odor. Your provider typically needs to observe at least three of these four markers to confirm the diagnosis. It’s worth getting checked rather than self-treating, because BV symptoms overlap with yeast infections and other conditions that require different treatment.
Reducing Your Risk
You can’t eliminate BV risk entirely, but several practical steps lower your chances:
- Skip douching entirely. It does more harm than good and is one of the most consistent risk factors for BV.
- Use condoms. They reduce your vagina’s exposure to alkaline semen and limit bacterial exchange with partners.
- Avoid scented products near the vagina. Fragrance-free soap on the external vulva is sufficient.
- Talk to your provider about partner treatment if BV keeps recurring, especially if you have a regular male sexual partner.
BV sits in an unusual gray zone: not a classic STI, but clearly influenced by sexual activity. Understanding that both sexual and non-sexual factors contribute helps explain why it’s so common and why it can affect virtually anyone with a vagina, regardless of their sexual history.