Bacterial vaginosis (BV) is considered a vaginal condition, not a sexually transmitted infection (STI). While that distinction might sound like semantics, it matters for how BV is understood, diagnosed, and treated. BV is the result of a shift in the vaginal microbiome, where protective bacteria decline and harmful bacteria overgrow. It affects roughly 23 to 29% of women of reproductive age worldwide, making it the most common vaginal condition in this group.
Why BV Is Not Classified as an STI
The CDC classifies BV as a “common, treatable, vaginal condition” rather than an STI. The reasoning comes down to cause: STIs are caused by specific pathogens passed between partners during sex. BV, on the other hand, results from an imbalance between the “good” and “harmful” bacteria already living in the vagina. No single organism causes it, and it can’t be traced to a specific transmission event the way chlamydia or gonorrhea can.
That said, BV has a complicated relationship with sexual activity. It most often occurs in people who are sexually active, and it rarely affects those who have never had sex. Having new or multiple sex partners increases the risk. So while sex is a contributing factor, BV itself isn’t something one partner “gives” to another in the traditional sense. Think of it more like a disruption triggered by changes in the vaginal environment, with sexual activity being one of several possible triggers.
What BV Actually Is: A Microbiome Imbalance
A healthy vagina is dominated by protective bacteria, primarily species of Lactobacillus. These bacteria produce lactic acid, keeping the vaginal pH low (acidic) and creating an environment that suppresses harmful microbes. In BV, those Lactobacillus populations drop sharply, and anaerobic bacteria (types that thrive without oxygen) overgrow to take their place. The most commonly identified of these is Gardnerella, though multiple species are usually involved.
This shift raises the vaginal pH above 4.5, which is one of the clinical markers doctors look for. The result is an environment that’s less acidic, less protected, and more hospitable to bacteria that can cause symptoms and other health problems. Researchers still don’t fully understand what triggers this shift in the first place, which is part of why BV remains classified as a condition rather than an infection with a clear cause.
Common Symptoms
Many people with BV have no symptoms at all. When symptoms do appear, the most recognizable ones include a thin, milky discharge that coats the vaginal walls and a noticeable fishy odor, which can be stronger after sex. The discharge tends to be grayish-white and has a consistency different from the thicker discharge associated with yeast infections.
BV does not typically cause itching, burning, or redness the way a yeast infection or STI might. If you’re experiencing those symptoms alongside unusual discharge, something else may be going on, either instead of or in addition to BV.
How BV Is Diagnosed
Doctors typically diagnose BV using a set of clinical signs known as the Amsel criteria. A positive diagnosis requires at least three of these four findings: thin, homogeneous discharge with a milklike consistency; the presence of “clue cells” (vaginal cells coated in bacteria) under a microscope; vaginal pH above 4.5; and a fishy odor when a chemical solution is applied to a sample of the discharge.
This means BV isn’t diagnosed by a single test or symptom. It’s identified by a pattern, which reflects its nature as a complex microbial shift rather than a straightforward infection.
Risk Factors
Several factors can disrupt the vaginal microbiome and increase the likelihood of developing BV:
- New or multiple sexual partners, which can introduce different bacteria and alter the vaginal environment
- Douching, which washes away protective Lactobacillus bacteria and raises vaginal pH
- Not using condoms, which may expose the vagina to bacteria or semen that shifts its pH
BV is more common in low-resource settings and areas with limited access to healthcare, suggesting that broader health and environmental factors also play a role.
Why It Matters Even Without Symptoms
Because BV often causes no obvious symptoms, it’s easy to dismiss as harmless. But untreated BV carries real health risks. Having BV increases your chances of acquiring other STIs, including HIV, likely because the loss of protective Lactobacillus leaves the vaginal lining more vulnerable to pathogens. During pregnancy, BV has been linked to preterm birth and other complications.
The recurrence rate is also notably high. Even after successful treatment, BV comes back in a significant number of cases, often within a few months. This is one of the most frustrating aspects of the condition and an area where medical understanding is still evolving.
How BV Is Treated
BV is treated with prescription antibiotics, available as either oral pills or vaginal gels or creams. Treatment courses are typically short, lasting around five to seven days. Most people see symptoms resolve within a few days of starting treatment.
If you’ve had BV before and recognize the symptoms, it’s still worth getting a proper diagnosis rather than assuming. The symptoms of BV overlap with yeast infections and some STIs, and treating the wrong condition won’t help and may make things worse. Because BV raises STI risk, confirming what you’re dealing with has implications beyond the immediate symptoms.