Bacterial vaginosis (BV) is not officially classified as a sexually transmitted infection. But if you’ve read the recent research about partners-with-penises carrying BV, you might think that answer doesn't quite capture the full story. And you're onto something, it doesn’t. BV sits in a weird gray area of sexual health, close enough to STIs that the two get confused constantly, different enough that doctors are careful not to call it one. 

Why BV isn't classified as an STI

STIs are defined by a specific, identifiable pathogen that passes from one person to another during sex, think the bacteria behind chlamydia or gonorrhea, or the virus behind herpes. BV doesn't fit that mold for a key reason: there's no single cause. BV happens when your vaginal microbiome tips out of balance, with protective lactobacilli getting crowded out by a mix of anaerobic bacteria, most commonly Gardnerella vaginalis, but often several others too.

BV also shows up in people who've never had sex, which is the biggest reason it hasn't been classified as an STI. If something can develop without any sexual contact at all, it can't be defined purely as sexually transmitted.

While BV isn't an STI, it's certainly connected to sexual activity, more than a lot of people realize:

• Having a new sexual partner or multiple partners raises your risk of BV.
• Sex without a condom is linked to higher BV rates.
• BV can occur in same-sex female couples at notably high rates, which points to something being exchanged during sex, not just heterosexual intercourse specifically.
• New research on male partners shows that BV-associated bacteria can live on penile skin and in the urethra without causing him any symptoms, and get passed back to his partner during sex. A 2025 clinical trial found that treating male partners alongside their partner with BV nearly cut recurrence in half.

That last point is part of why some researchers are now calling BV an "overlooked STI" and pushing for more research into partner treatment.

What actually separates BV from an STI?

STIs are caused by one specific organism. BV is caused by a shift in your entire bacterial ecosystem, which can be triggered by sex, but also by hormonal changes, smoking, douching, or an IUD.

BV is incredibly common and not always about sex. An estimated one in three people with a vagina will experience BV at some point. It's the most common vaginal condition in people of reproductive age, and it can happen even in periods of no sexual activity.

Testing and treatment protocols differ. STIs typically come with partner notification requirements and standard partner treatment protocols. BV, historically, hasn't, though that may start to shift as the partner-treatment research develops.

So even though BV won't show up on an STI panel and doesn't carry the same stigma, it deserves the same seriousness. It's not "just" an imbalance, and it's not something to shrug off if it keeps coming back.

BV isn't an STI, but it isn't entirely unrelated to sex, either. It lives in its own category… a common, treatable condition that's influenced by your microbiome, your hormones, your habits, and sometimes your partner. Understanding that nuance is the difference between dismissing recurring BV as bad luck and actually getting to the bottom of it.

Questions about BV, testing, or what to try next? We're here for it. Check out our Vaginal Health Test + Treat to figure out what you're dealing with, and our Male BV Treatment to keep the infection from coming back!