Bacterial vaginosis (BV) is a vaginal condition caused by an imbalance in the bacteria that naturally live in the vagina. It affects roughly 23 to 29 percent of women of reproductive age worldwide, making it the most common vaginal condition in that age group. BV is not a sexually transmitted infection, though sexual activity can increase the risk of developing it.
What Happens Inside the Vagina
A healthy vagina is home to a community of bacteria dominated by Lactobacillus species. These bacteria produce lactic acid, hydrogen peroxide, and other antimicrobial substances that keep the vaginal environment acidic (typically below a pH of 4.5) and inhospitable to harmful organisms. This acidic environment is essentially the vagina’s built-in defense system.
In BV, Lactobacillus populations drop and are replaced by an overgrowth of anaerobic bacteria, organisms that thrive in low-oxygen environments. The main culprits include Gardnerella, Atopobium, Prevotella, and Sneathia. These bacteria produce short-chain fatty acids that raise vaginal pH above 4.5, making the environment less acidic and less protective. They also break down amino acids and mucosal proteins, which produces amine compounds responsible for BV’s characteristic odor and thins the protective mucosal lining of the vaginal tract.
Gardnerella and related bacteria can form a biofilm, a sticky layer of organisms that adheres to vaginal cells. This biofilm is one reason BV can be stubborn to treat and tends to come back. It shields the bacteria from both antibiotics and the body’s natural defenses.
Symptoms and What BV Feels Like
Many people with BV have no symptoms at all. When symptoms do appear, the most common ones include:
- Discharge: A thin, white or gray vaginal discharge that looks uniform rather than clumpy
- Odor: A strong fish-like smell, often more noticeable after sex
- Irritation: Mild itching or burning around the vaginal opening, though this is less common than with yeast infections
The fishy smell comes directly from the amines produced when anaerobic bacteria break down proteins in the vaginal lining. Sex can make the odor stronger because semen is alkaline, which triggers more amine release. This is one of the more distinctive features that sets BV apart from other vaginal infections. Yeast infections, by comparison, typically produce a thick, white, cottage cheese-like discharge with itching but little odor.
What Increases Your Risk
BV is not caused by poor hygiene. In fact, overcleaning can be part of the problem. Douching is one of the most well-established risk factors because it disrupts the natural bacterial balance and washes away protective Lactobacillus. Other factors that shift the vaginal environment toward BV include having a new sexual partner or multiple partners, using scented soaps or products inside or around the vagina, and not using condoms.
Hormonal changes can also play a role. Anything that alters the vaginal environment, whether it’s a new contraceptive, menstruation, or pregnancy, can create conditions where anaerobic bacteria gain a foothold. Some people experience recurrent BV despite avoiding known triggers, which likely reflects individual differences in their vaginal microbiome’s resilience.
How BV Is Diagnosed
Diagnosing BV typically happens in a clinic visit using a set of bedside findings known as the Amsel criteria. A clinician looks for at least three of these four signs:
- A thin, uniform, gray-white or yellowish discharge
- Vaginal pH above 4.5
- A fishy odor released when a chemical solution is added to a sample of the discharge (called the whiff test)
- The presence of “clue cells” under a microscope, which are vaginal cells coated with a layer of bacteria that gives them a grainy, stippled appearance
A more precise lab method called the Nugent score involves staining a vaginal sample and counting the relative amounts of Lactobacillus, Gardnerella, and curved bacteria under a microscope. This scoring system is considered the gold standard for research, though the Amsel criteria are more practical for a routine office visit. Either way, the diagnosis is straightforward and doesn’t require blood tests or imaging.
Treatment Options
BV is treated with antibiotics that target anaerobic bacteria. The standard options are oral pills taken twice daily for seven days or a vaginal gel or cream applied for five to seven days. Both oral and topical routes are effective, and the choice often comes down to personal preference. Some people find vaginal treatment easier to tolerate since it avoids common oral antibiotic side effects like nausea.
Treatment typically clears symptoms within a few days, though it’s important to finish the full course even after symptoms improve. Stopping early increases the chance that the biofilm-forming bacteria survive and the infection returns.
Why BV Keeps Coming Back
Recurrence is the most frustrating aspect of BV. More than half of people treated for BV experience a recurrence within 12 months. The bacterial biofilm that forms on vaginal cells is a major reason: antibiotics reduce the bacterial load enough to relieve symptoms, but the biofilm can persist and serve as a reservoir for regrowth.
For recurrent BV, some providers recommend extended or suppressive antibiotic therapy following the initial treatment course. Probiotics containing Lactobacillus strains have been studied as a way to help restore the vaginal microbiome, but results have been mixed, likely because the biofilm makes it difficult for beneficial bacteria to recolonize. Practical steps that may help reduce recurrence include avoiding douching, using condoms, and switching away from scented products in the genital area.
Potential Complications
BV that goes untreated or keeps recurring can raise the risk of several health problems. The disrupted vaginal lining and reduced acidity make it easier for sexually transmitted infections, including HIV, chlamydia, and gonorrhea, to take hold. BV also increases the risk of pelvic inflammatory disease, an infection of the uterus and fallopian tubes that can affect fertility.
During pregnancy, BV is linked to preterm birth, low birth weight, and premature rupture of membranes. Pregnant people who notice BV symptoms should bring them up at their next prenatal visit, since treatment during pregnancy can reduce these risks. BV can also increase the chance of infection after gynecological procedures like IUD insertion or hysterectomy.