Bacterial vaginosis (BV) is not a classic infection caused by a single invading germ. It’s better described as a disruption of the vaginal microbiome, where the protective bacteria decline and other bacteria overgrow. That distinction matters because it shapes how BV is treated, why it comes back so often, and why antibiotics alone don’t always solve the problem.
Why BV Doesn’t Fit the Typical Definition of an Infection
A standard infection involves a specific pathogen entering the body and causing disease. BV doesn’t work that way. No single bacterium has been identified as the cause, and it fails the classic test (known as Koch’s postulates) that scientists use to link a specific microbe to a specific disease. Instead, BV involves a shift in the entire bacterial community living in the vagina. Hydrogen peroxide-producing lactobacilli, which normally keep the environment acidic and inhospitable to harmful organisms, decline in number. That opens the door for anaerobic bacteria, particularly Gardnerella species, to multiply rapidly.
Medically, this type of shift is called dysbiosis rather than infection. But the picture is more complicated than that label suggests. Recent research using advanced imaging has revealed that Gardnerella and other bacteria can form a structured biofilm, a sticky colony that adheres to the vaginal lining and resists treatment. This biofilm behaves more like an active infection than a simple imbalance, and it’s linked to complications like ascending reproductive tract infections, preterm birth, and infertility. Many researchers now consider BV a syndrome that includes both biofilm-driven disease and other forms of microbial disruption that haven’t been fully characterized yet.
BV Is Not a Sexually Transmitted Infection
BV is not classified as an STI. The CDC states that the cause of the microbial shift behind BV is not fully understood, and whether it results from acquiring a single sexually transmitted pathogen remains unknown. BV can occur in people who have never had sex, though it rarely does. Sexual activity is the strongest associated factor, and having multiple partners increases risk, but the relationship isn’t the straightforward transmission pattern seen with STIs like chlamydia or gonorrhea.
Other factors that raise BV risk include douching, which disrupts the vaginal bacterial balance, and changes in hygiene products. Because BV is so closely tied to sexual activity without being definitively sexually transmitted, it occupies an awkward gray zone that can be confusing for both patients and clinicians.
What BV Feels Like
The hallmark symptom is a thin, grayish-white discharge with a strong fishy odor, especially noticeable after sex. Some people also experience mild itching or burning during urination. But roughly half of people with BV have no symptoms at all, which means it can persist unnoticed for weeks or months.
A healthcare provider can diagnose BV by checking vaginal pH (a reading above 4.5 suggests BV, since healthy vaginal pH is more acidic), examining discharge under a microscope for characteristic “clue cells,” and noting the fishy odor when a chemical solution is added to a sample.
Why It Matters Even Without Symptoms
Untreated BV raises the risk of several complications. During pregnancy, BV roughly doubles the odds of preterm birth, with a meta-analysis calculating an overall relative risk of 1.44 to 1.79 depending on the measure used. Outside of pregnancy, BV makes you more susceptible to STIs including HIV, chlamydia, and gonorrhea, because the loss of protective lactobacilli weakens one of the body’s natural barriers to those pathogens. BV is also associated with pelvic inflammatory disease, which can affect fertility.
Treatment and the Recurrence Problem
BV is treated with prescription antibiotics, typically taken orally or applied as a vaginal gel or cream. Most people see symptoms resolve within a few days of starting treatment. The bigger challenge is keeping BV from coming back. Recurrence rates are strikingly high: up to 69% of people experience a return of BV within 12 months of completing standard treatment. This is one of the strongest arguments that BV isn’t a simple infection. If it were, antibiotics would typically clear it for good. Instead, the biofilm and underlying microbial disruption often survive treatment and re-establish themselves.
This high recurrence rate has driven significant interest in probiotics as an add-on or alternative approach. A meta-analysis of randomized controlled trials found that combining probiotics with antibiotics produced a cure rate of about 73%, compared to 63% with antibiotics alone. Probiotics given on their own cured roughly 56% of cases versus near-zero improvement with placebo, and their cure rates were statistically comparable to antibiotics in head-to-head comparisons. High-dose formulations (at least 1 billion colony-forming units) were more effective than lower doses, and oral probiotics appeared to work better than vaginal application. The strains most commonly studied include various Lactobacillus species, the same family of bacteria that BV displaces.
Reducing Your Risk
Because BV stems from disruption of vaginal bacteria rather than a single transmissible germ, prevention focuses on protecting that bacterial ecosystem. Avoiding douching is the most consistently recommended step, since douching washes away the lactobacilli that maintain a healthy acidic environment. Using condoms may help reduce recurrence, given the strong link between sexual activity and BV. Avoiding scented soaps, sprays, and other products in the vaginal area also helps maintain microbial balance.
If you experience recurrent BV, it’s worth discussing a longer or combination treatment approach with your provider, since the standard short-course antibiotic regimen clearly falls short for many people. The fact that BV recurrence rates remain so high with current treatments reflects how much is still being worked out about what drives this condition and how best to address the underlying microbial disruption rather than just suppressing symptoms.