Bacterial vaginosis, commonly called BV, is the most common vaginal infection in women ages 15 to 44. It happens when the balance between protective and harmful bacteria in the vagina shifts, allowing organisms that are normally present in small numbers to overgrow. BV is not a sexually transmitted infection, though sexual activity can increase the risk of developing it.
What Causes the Bacterial Imbalance
A healthy vagina is dominated by bacteria called lactobacilli. These produce lactic acid that keeps the vaginal pH below 4.5, creating an environment hostile to most harmful microbes. They also physically coat the vaginal lining, forming a barrier against invaders. When lactobacilli decline, other bacteria, particularly one called Gardnerella vaginalis, multiply and form sticky biofilms along the vaginal walls. This shift is what produces BV symptoms.
Several factors can trigger this imbalance. Douching is one of the most well-established risks because it strips away protective bacteria. Having new or multiple sexual partners and not using condoms also disrupts vaginal flora. BV can occur in women who have never had sex, though it’s less common. The exact chain of events that tips the balance isn’t fully understood, which is part of why recurrence rates are so high.
Symptoms to Recognize
The hallmark symptom is a thin, grayish-white discharge with a noticeable fishy smell. The odor often becomes stronger after sex or during a period. The discharge tends to be uniform and milky in consistency, coating the vaginal walls smoothly rather than clumping.
Some women also notice mild itching or burning during urination, though these symptoms are more commonly associated with yeast infections or urinary tract infections. Roughly half of women with BV have no symptoms at all, which means the infection can persist without being noticed.
How BV Is Diagnosed
Doctors typically diagnose BV using a set of bedside checks. A clinician looks for four things: the characteristic thin, homogeneous discharge; a vaginal pH above 4.5; a fishy odor when a chemical solution is applied to a sample (sometimes called the “whiff test”); and the presence of “clue cells” under a microscope, which are vaginal cells visibly coated with bacteria. If three of these four signs are present, the diagnosis is BV.
Lab-based testing offers another route. A scoring system grades a vaginal sample on a scale from 0 to 10 based on the types of bacteria visible under a microscope. Scores of 0 to 3 indicate a normal, lactobacillus-dominant environment. Scores of 4 to 6 fall into an intermediate range. A score of 7 to 10 confirms BV, showing significant loss of lactobacilli and overgrowth of harmful bacteria.
Why BV Matters Beyond Discomfort
BV isn’t just a nuisance. It raises the risk of acquiring sexually transmitted infections, including HIV, because the disrupted vaginal lining is more vulnerable to pathogens. It can also increase the likelihood of complications after gynecological procedures.
During pregnancy, the stakes are higher. A meta-analysis found that women with BV face roughly 1.4 to 1.8 times the risk of preterm delivery compared to women without it. That elevated risk makes screening and treatment during pregnancy particularly important.
Treatment and What to Expect
BV is treated with prescription antibiotics, most commonly taken either orally or applied as a vaginal gel or cream. Treatment courses typically last five to seven days. Symptoms usually improve within a few days, and most women feel fully better by the time they finish the course. It’s important to complete the entire prescription even if symptoms resolve early, since stopping short can leave enough harmful bacteria behind to trigger a relapse.
The bigger challenge with BV is that it comes back frequently. More than 50% of women who complete standard antibiotic treatment experience a recurrence within three to six months. Over a full year, recurrence rates climb as high as 69%. This isn’t a failure of treatment so much as a reflection of how difficult it is to fully restore a healthy vaginal microbiome once it’s been disrupted. Gardnerella biofilms are stubborn, and antibiotics can kill free-floating bacteria without fully penetrating the biofilm structure.
Reducing the Risk of Recurrence
Because recurrence is so common, prevention matters as much as treatment. The basics are straightforward: avoid douching, use condoms with new partners, and limit the number of products (soaps, sprays, scented wipes) that come into contact with the vaginal area. These steps won’t guarantee protection, but they remove some of the most common triggers.
Probiotics are an area of growing interest. The logic is simple: if BV results from losing protective lactobacilli, reintroducing them should help. The most promising research involves a specific strain of Lactobacillus crispatus delivered vaginally after antibiotic treatment. In a randomized, placebo-controlled trial of 228 women, those who used the probiotic had a 30% recurrence rate at 12 weeks compared to 45% in the placebo group. Nearly 80% of treated participants showed successful colonization of the protective bacteria.
Other lactobacillus strains have shown the ability to lower vaginal pH, improve bacterial balance scores, and even disrupt Gardnerella biofilms in laboratory studies. These bacteria work through several mechanisms: producing lactic acid to maintain acidity, releasing natural antimicrobial compounds, and physically competing with harmful bacteria for space on the vaginal lining. Probiotics are not a replacement for antibiotics during an active infection, but they show real potential as a follow-up strategy to keep BV from returning.
BV vs. Yeast Infections
Many women confuse BV with a yeast infection because both cause vaginal discomfort. The differences are fairly reliable. Yeast infections produce thick, white, clumpy discharge (often compared to cottage cheese) and significant itching, but usually no strong odor. BV produces thin, grayish discharge with a fishy smell and less itching. Yeast infections are caused by fungal overgrowth, while BV is purely bacterial. This distinction matters because they require completely different treatments. Over-the-counter antifungal products won’t touch BV, and using them when you actually have BV just delays proper care.