Bacterial vaginosis (BV) happens when the balance of bacteria inside the vagina shifts. Normally, beneficial bacteria called lactobacilli dominate the vaginal environment, producing lactic acid and hydrogen peroxide that keep harmful bacteria in check. When those protective bacteria get displaced by a mix of anaerobic bacteria, the result is BV. It’s the most common vaginal condition in people of reproductive age, and despite how frequently it occurs, researchers still don’t fully understand every trigger.
What Actually Happens Inside the Vagina
A healthy vagina has an acidic environment, maintained primarily by lactobacilli. These bacteria act as a natural defense system. BV starts when certain strains of harmful bacteria, particularly one called Gardnerella vaginalis, begin to displace those lactobacilli and form a sticky layer called a biofilm on the vaginal walls.
From there, the process cascades. Gardnerella breaks down proteins in the vaginal lining, which promotes the growth of another bacterium called Prevotella. These two organisms feed off each other: Prevotella produces ammonia that helps Gardnerella thrive, and together they degrade the protective mucus layer of the vaginal wall. Once that barrier is compromised, other anaerobic bacteria pile on and join the biofilm. The vaginal pH rises from its normal acidic range to a more alkaline level, and you end up with the symptoms most people associate with BV: thin grayish-white discharge and a strong, fishy odor.
The Main Risk Factors
BV occurs most often in people who are sexually active. Having a new sexual partner or multiple partners is one of the strongest risk factors, though researchers still don’t fully understand the exact mechanism by which sex triggers the bacterial shift. It is not classified as a sexually transmitted infection, but sexual activity clearly plays a role in disrupting the vaginal microbiome.
Not using condoms also increases your risk. Condoms appear to help maintain the balance of vaginal bacteria, possibly by preventing the introduction of outside bacteria or by keeping semen (which is alkaline) from shifting vaginal pH.
Beyond sexual activity, several other factors can set the stage for BV:
- Douching. This is one of the most well-documented triggers. Rinsing the inside of the vagina with water or cleansing products washes away lactobacilli and disrupts the natural bacterial balance. The World Health Organization specifically advises against vaginal douching and excessive vaginal cleansing.
- Intravaginal products. Inserting herbs, scented soaps, or other products into the vagina can have a similar disruptive effect.
- Smoking. Cigarette smoking has a dose-dependent relationship with BV risk, meaning the more you smoke, the higher the risk. Research published in the American Journal of Obstetrics & Gynecology found that smokers have a measurably different vaginal metabolic environment compared to nonsmokers, though the exact mechanism linking tobacco to BV is still being studied.
Can You Get BV Without Having Sex?
Yes. While sexual activity is the most common context, BV can develop in people who have never had sex. Anything that disrupts the lactobacilli-dominated environment can potentially trigger it. Douching alone can do it. Hormonal changes, antibiotic use (which can kill off protective bacteria along with harmful ones), and even the natural fluctuations of the menstrual cycle can all shift the bacterial balance enough to open the door to BV.
What BV Feels Like
Many people with BV have no symptoms at all. When symptoms do appear, the most common is a thin, off-white or grayish discharge with a noticeable fishy smell, especially after sex. Some people experience mild itching or burning during urination, but BV is generally not painful. The smell is often what prompts people to seek help.
BV is diagnosed through a pelvic exam. Your provider will check your vaginal pH (which rises above 4.5 with BV), examine the discharge under a microscope, and may perform a “whiff test” where a chemical is added to a sample of discharge to see if it produces a fishy odor. These signs together paint a clear picture.
How BV Is Treated
BV is treated with antibiotics, typically taken orally or applied as a vaginal gel or cream. Treatment courses usually last about five to seven days. Most people notice improvement within a few days of starting treatment. You don’t need to treat a male sexual partner, though there is ongoing research into whether treating partners might reduce recurrence.
The bigger challenge with BV is that it comes back. Within 6 to 12 months of finishing antibiotic treatment, 50% to 80% of people will experience a recurrence. This high recurrence rate is likely related to the biofilm that forms during infection. Antibiotics can reduce the overgrown bacteria, but remnants of the biofilm may persist on the vaginal walls, giving harmful bacteria a foothold to regrow.
Reducing Your Risk of Getting BV Again
Because recurrence is so common, prevention matters as much as treatment. The most effective steps are straightforward:
- Stop douching entirely. The vagina is self-cleaning. Warm water on the outside is enough.
- Avoid scented products near the vagina. This includes scented soaps, bubble baths, and sprays.
- Use condoms consistently. This reduces exposure to bacteria and alkaline semen that can shift vaginal pH.
- Limit the number of sexual partners. Each new partner introduces a different bacterial profile.
- Quit smoking if you currently smoke. Given the dose-dependent relationship between smoking and BV, reducing or eliminating tobacco use lowers your risk.
Some research suggests that probiotics may help reduce BV recurrence, and early meta-analyses have found statistically significant reductions in recurrence rates with probiotic use. However, the evidence is still developing, and there’s no consensus yet on which specific strains or delivery methods work best. Oral and vaginal probiotic supplements containing lactobacillus strains are the most commonly studied.
Why BV Shouldn’t Be Ignored
BV isn’t just uncomfortable. The loss of the protective mucus layer and the shift to an alkaline vaginal environment make you more vulnerable to sexually transmitted infections, including HIV and herpes. During pregnancy, untreated BV is associated with preterm birth and low birth weight. Even outside of pregnancy, the chronic inflammation caused by recurring BV can affect reproductive health over time.
If you notice a change in your discharge, particularly if it has a fishy smell, getting tested is simple and treatment is effective. The real goal is identifying what’s disrupting your bacterial balance so you can break the cycle of recurrence.