Bacterial vaginosis (BV) happens when the balance of bacteria inside your vagina shifts. Normally, beneficial bacteria called lactobacilli dominate and keep the environment acidic, which prevents other organisms from taking over. When those protective bacteria decline and are replaced by a surge of other microbes, the result is BV. It’s the most common vaginal condition in women of reproductive age, and the frustrating truth is that there’s rarely one single cause you can point to.
What’s Actually Happening Inside Your Body
Your vagina maintains its own ecosystem. Lactobacilli break down glycogen (a sugar stored in vaginal tissue) into lactic acid, keeping the pH low and acidic. That acidic environment acts like a natural defense system, suppressing the growth of harmful organisms. BV develops when lactobacilli sharply decline and anaerobic bacteria, organisms that thrive without oxygen, multiply to take their place.
The bacterium most consistently linked to BV is Gardnerella vaginalis. What makes it particularly effective is its ability to physically attach to vaginal cells, push aside protective lactobacilli, and build a biofilm: a sticky, structured layer of bacteria that coats the vaginal lining. In biopsies of women with BV, this biofilm was present on 90% of the vaginal surfaces examined. Once that biofilm is established, Gardnerella pulls other anaerobic species into the community, creating a self-reinforcing colony that’s harder for your body (and antibiotics) to clear.
This biofilm is also a major reason BV keeps coming back. The bacteria inside it are far more tolerant of lactic acid and hydrogen peroxide than free-floating bacteria, meaning they can survive even when lactobacilli try to recolonize. It’s not that your body fails to fight back. It’s that the biofilm gives the harmful bacteria a fortified position.
Common Triggers and Risk Factors
BV isn’t caused by poor hygiene. In fact, overcleaning is more likely to be a problem. Douching is associated with a 20% higher incidence of BV, likely because flushing the vaginal canal disrupts the bacterial balance. Interestingly, one small study found that stopping douching for four weeks didn’t immediately reduce BV risk, suggesting the damage to the microbiome may take longer to reverse.
Sexual activity is one of the strongest risk factors, though BV is not classified as a sexually transmitted infection. New sexual partners, multiple partners, and unprotected sex all increase your chances. Semen is alkaline, so exposure can temporarily raise your vaginal pH, creating a window where anaerobic bacteria have an easier time gaining ground. Using condoms or dental dams reduces this effect by keeping your partner’s bodily fluids from altering your pH.
Other things that can tip the balance:
- Scented soaps, bubble baths, or vaginal deodorants can irritate tissue and alter bacteria
- Copper IUDs have been linked to elevated BV risk in prospective studies, though hormonal IUDs don’t show the same association
- Smoking is consistently associated with higher BV rates, though the exact mechanism isn’t fully understood
- Antibiotics taken for other infections can inadvertently reduce lactobacilli
How Hormones Play a Role
Estrogen is the behind-the-scenes manager of your vaginal ecosystem. When estrogen levels are high, your vaginal cells mature faster and store more glycogen. More glycogen means more fuel for lactobacilli, more lactic acid production, and a lower, more protective pH. This is why BV is most common during reproductive years when hormonal fluctuations are constant.
Any time estrogen drops, the environment becomes less hospitable for lactobacilli. This happens during certain phases of your menstrual cycle, during breastfeeding, and during perimenopause. Some women notice BV symptoms flare right after their period, when both estrogen and the vaginal pH are temporarily shifted. Pregnancy, on the other hand, brings high estrogen levels that generally support lactobacilli, though the increased glycogen can sometimes create its own complications.
Why Some People Get BV More Than Others
There are real disparities in who develops BV, and they aren’t fully explained by behavior. In one large study, 45% of African American women tested positive for BV compared to 17% of white American women. Low income was significantly associated with higher BV prevalence among African American women, pointing to a web of factors including chronic stress, neighborhood environment, and access to healthcare rather than any simple biological explanation.
Genetics also influence which bacterial communities naturally colonize your vagina. Some women have vaginal microbiomes that are less dominated by lactobacilli even in the absence of BV, which may make them more vulnerable to shifts. This is part of why BV can feel so arbitrary: two people with the same habits and exposures can have very different experiences.
How BV Is Identified
The classic signs are a thin, grayish-white discharge with a noticeable fishy smell, often stronger after sex or during your period. But about half of women with BV don’t have obvious symptoms, which is why it sometimes shows up unexpectedly on a routine exam.
Clinicians typically look for at least three of four markers: the characteristic thin discharge, a vaginal pH above 4.5, the presence of “clue cells” (vaginal cells coated in bacteria visible under a microscope), and a fishy odor. You can’t reliably diagnose BV on your own because other conditions like yeast infections and trichomoniasis can overlap in symptoms.
What Treatment Looks Like
BV is treated with antibiotics, either taken orally or applied as a vaginal gel or cream. A standard course runs about five to seven days, and symptoms usually improve within a few days of starting. The challenge isn’t the initial treatment. It’s recurrence. Roughly half of women who are treated for BV will have it return within 12 months.
That high recurrence rate ties directly back to the biofilm. Antibiotics kill the free-floating bacteria effectively, but the biofilm on the vaginal wall can persist, seeding a new infection once treatment stops. This is an active area of medical interest, and some clinicians now use extended or suppressive treatment courses for women who experience frequent recurrences.
If you’re dealing with recurring BV, it’s worth examining your specific risk factors: contraception type, sexual practices, products you use in or around your vagina. Small changes like switching from a copper IUD to a hormonal one, using condoms consistently, or eliminating scented products can shift the odds in your favor, even if no single change is a guaranteed fix.