Bacterial vaginosis (BV) happens when the balance of bacteria inside the vagina shifts. Normally, beneficial bacteria called lactobacilli keep the vaginal environment slightly acidic, which prevents harmful bacteria from taking over. When those protective bacteria decline and other types multiply in their place, the result is BV. It’s the most common vaginal condition in women of reproductive age, and despite how often it occurs, the exact trigger isn’t always obvious.
What Actually Happens Inside the Vagina
A healthy vagina maintains an acidic pH, typically below 4.5, thanks to lactobacilli. These bacteria produce compounds that suppress the growth of other organisms. BV develops when lactobacilli drop in number and a mix of other bacteria fills the gap. The vaginal pH rises above 4.5, creating an environment where these organisms thrive.
Two types of bacteria in particular tend to team up during BV. Together, they form a sticky layer called a biofilm on the vaginal walls. This biofilm is a big part of why BV can be so stubborn: it shields the bacteria from both the body’s natural defenses and from treatment, making infections more likely to persist or come back.
Common Causes and Risk Factors
There’s no single cause of BV. Instead, several factors can tip the bacterial balance in the wrong direction.
Sexual activity is one of the strongest associations. New partners, multiple partners, and unprotected sex all correlate with higher BV rates. BV is not classified as a sexually transmitted infection because it can occur in people who have never had sex, but sexual activity clearly changes the vaginal environment in ways that make BV more likely. Semen, for example, is alkaline and temporarily raises vaginal pH.
Douching is one of the most well-documented risk factors. According to the U.S. Department of Health and Human Services, douching removes some of the normal bacteria that protect against infection and can cause an overgrowth of harmful bacteria. A healthy vagina cleans itself through natural discharge, so douching disrupts a system that’s already working.
Scented products near the vagina, including scented tampons, pads, powders, and sprays, can also increase the chance of infection. These products introduce chemicals that irritate the vaginal lining and alter its natural chemistry.
Antibiotics taken for other infections can inadvertently kill off lactobacilli along with whatever they’re targeting, leaving the vagina vulnerable to BV. Smoking, hormonal changes, and IUD use have also been linked to higher risk, though the mechanisms are less clear.
Signs You Might Have BV
Many people with BV have no symptoms at all. When symptoms do appear, the most recognizable one is a thin, grayish-white discharge with a noticeable fishy smell. The odor often becomes stronger after sex. The discharge tends to be watery and milklike in consistency, coating the vaginal walls evenly rather than appearing thick or clumpy (which is more typical of a yeast infection).
Some people also notice mild itching or burning, particularly during urination, though these symptoms are less common with BV than with other vaginal infections. If you’re unsure whether you’re dealing with BV or something else, the distinction matters because the treatments are different.
How BV Is Diagnosed
A healthcare provider can usually diagnose BV during a routine exam using a few straightforward checks. They’ll look at the consistency of the discharge, test the vaginal pH (anything above 4.5 is a flag), examine a sample under a microscope for cells coated in bacteria, and check for a fishy odor. Meeting three of these four criteria confirms the diagnosis. The whole process takes just a few minutes and doesn’t require blood work or imaging.
Why BV Shouldn’t Be Ignored
Untreated BV isn’t just uncomfortable. It raises the risk of more serious problems. More than 85% of pelvic inflammatory disease (PID) cases are caused by BV-related bacteria or sexually transmitted infections. PID is an infection of the uterus, fallopian tubes, or ovaries that can lead to chronic pelvic pain and fertility problems. Even a milder form of this, called subclinical PID, where bacteria travel upward without causing obvious symptoms, is 2.7 times more common in women with BV.
BV also makes you more susceptible to sexually transmitted infections, including HIV, chlamydia, and gonorrhea. During pregnancy, BV has been associated with preterm birth and low birth weight, which is why some providers screen for it during prenatal care.
Treatment and What to Expect
BV is treated with prescription antibiotics, available as either oral pills or vaginal gels and creams. A typical course lasts five to seven days. Most people notice improvement within a couple of days, but finishing the full course is important to reduce the chance of the bacteria bouncing back.
The frustrating reality of BV is its recurrence rate. Within 6 to 12 months of finishing antibiotic treatment, 50% to 80% of women experience BV again. This is partly because of that biofilm: antibiotics can reduce the harmful bacteria but may not fully destroy the protective layer they’ve built. For people dealing with repeated infections, providers sometimes recommend extended or suppressive treatment strategies.
Reducing Your Risk
You can’t guarantee you’ll never get BV, but several habits help keep the vaginal environment stable.
- Skip the douche. The vagina is self-cleaning. Douching washes away the very bacteria you need.
- Avoid scented products. Fragrance-free tampons, pads, and soaps reduce chemical irritation.
- Wear cotton underwear. Cotton wicks away moisture that bacteria thrive on. The Cleveland Clinic recommends 100% cotton and changing your underwear at least once daily, more often if they become damp.
- Go commando at night. Sleeping without underwear or in loose pajamas increases airflow and helps the area stay dry.
- Use condoms. Barrier methods reduce the introduction of new bacteria and prevent alkaline semen from shifting vaginal pH.
- Choose the right detergent. Hypoallergenic, fragrance-free, dye-free detergents are gentler on sensitive skin. Washing new underwear before wearing it also removes manufacturing chemicals.
Probiotics marketed for vaginal health are widely available, but the evidence supporting their ability to prevent BV recurrence is still limited and inconsistent. They’re unlikely to cause harm, but they shouldn’t replace proven strategies like avoiding douching and using condoms.