Bacterial vaginosis, commonly called BV, is the most common vaginal infection in women of reproductive age. It happens when the balance of bacteria inside the vagina shifts: the protective bacteria that normally dominate decline sharply, and other types of bacteria multiply to take their place. BV is not a sexually transmitted infection, though sexual activity can increase the risk. It often causes a noticeable discharge and odor, but many women have no symptoms at all.
What Happens Inside the Vagina
A healthy vaginal environment is dominated by bacteria called Lactobacillus, which produce antimicrobial compounds that keep other microbes in check. Think of them as the gatekeepers. In BV, the number of Lactobacillus drops dramatically and anaerobic bacteria (types that thrive without oxygen) take over. The most common one found in BV is Gardnerella vaginalis, which can form a protective film called a biofilm on the vaginal walls, sheltering itself and other harmful bacteria from the body’s defenses.
Having Gardnerella in the vagina doesn’t automatically mean you have BV. Many women carry it without problems. BV develops when the overall microbial balance tips far enough that the protective bacteria can no longer keep the anaerobes under control.
Common Symptoms
The hallmark signs of BV are a thin white or gray vaginal discharge and a strong fishy odor, especially noticeable after sex. The odor comes from chemical compounds called amines that the overgrown bacteria produce. Unlike a yeast infection, BV typically doesn’t cause significant itching, redness, or thick clumpy discharge.
Up to half of women with BV have no symptoms. In those cases, it may only be detected during a routine gynecological exam. If you do notice a change in discharge or an unusual smell, that’s worth bringing up with your provider, since the symptoms can overlap with other vaginal infections that require different treatment.
What Increases Your Risk
Several factors make BV more likely. Having a new sexual partner or multiple partners is one of the strongest associations, though BV also occurs in women who have never been sexually active. Douching is a well-established risk factor because it strips away the protective Lactobacillus and disrupts the vagina’s natural pH. Using scented soaps or products inside the vagina can have a similar effect. Smoking, hormonal changes, and the use of certain IUDs have also been linked to higher BV rates.
The vagina is self-cleaning, so the simplest way to protect its bacterial balance is to avoid inserting soaps, fragrances, or cleansing products into it.
How BV Is Diagnosed
Diagnosis usually happens in a clinic. Your provider will look at the characteristics of the discharge, test its pH (BV raises vaginal pH above the normal acidic range), and may examine a sample under a microscope. A lab scoring method called the Nugent score can confirm the diagnosis by counting the relative numbers of healthy and harmful bacteria in the sample. The process is straightforward and typically done in a single office visit.
Treatment Options
BV is treated with antibiotics, either taken by mouth or applied as a vaginal gel or cream. The most commonly prescribed options are oral metronidazole (a pill taken twice daily for seven days), metronidazole vaginal gel (applied once daily for five days), or clindamycin vaginal cream (applied at bedtime for seven days). All three are considered equally effective first-line treatments.
If one of those doesn’t work or isn’t tolerated well, alternatives include tinidazole (a related oral antibiotic) or oral clindamycin. Most women notice improvement within a few days, and symptoms typically resolve completely by the end of the treatment course. It’s important to finish the full course even if symptoms clear up early.
Why BV Keeps Coming Back
Recurrence is one of the most frustrating aspects of BV. Research tracking women for a full year after successful antibiotic treatment found that 43% had a recurrence by three months, 52% by six months, and 58% by twelve months. Nearly one in four women had a recurrence within the first month alone. These are high numbers, and they help explain why BV can feel like a chronic problem for many women.
The biofilm that Gardnerella builds on the vaginal wall is one likely reason antibiotics don’t always produce lasting results. The biofilm can persist even after the bacteria floating freely in the vagina are killed, allowing the infection to re-establish itself once treatment stops.
Probiotics for Prevention
There is growing interest in using probiotics, specifically Lactobacillus strains, to help prevent BV from returning after antibiotic treatment. One clinical trial tested vaginal capsules containing Lactobacillus crispatus in women with recurrent BV (at least two episodes in the past year). Women who used the probiotic capsules during four menstrual cycles after completing antibiotics had a recurrence rate of about 21%, compared to 41% in the placebo group. The time before BV came back was also about 28% longer in the probiotic group.
These results are encouraging but modest. Probiotics aren’t a guaranteed fix, and not all probiotic products contain the specific strains studied. If you’re dealing with recurring BV, this is worth discussing with your provider as a complement to antibiotic treatment rather than a replacement.
BV and Pregnancy
BV during pregnancy carries real risks. A large meta-analysis found that women with BV have roughly 1.6 times the odds of delivering preterm compared to women without it, and some earlier analyses put that figure even higher, around a twofold increase. The leading theory is that bacteria from the vagina can travel upward to the membranes surrounding the fetus, triggering early labor or premature rupture of those membranes.
Because of these risks, pregnant women who develop symptoms of BV are typically treated with antibiotics. The treatment options are similar to those for non-pregnant women, though your provider will choose the regimen best suited to pregnancy.
BV and Susceptibility to Other Infections
When the protective Lactobacillus population is depleted, the vaginal environment becomes more vulnerable. Women with BV have a higher risk of acquiring sexually transmitted infections, including chlamydia, gonorrhea, and HIV. The disrupted bacterial balance and higher pH reduce the vagina’s natural chemical defenses, making it easier for pathogens to establish themselves. Treating BV isn’t just about relieving symptoms; it’s also about restoring a layer of biological protection.