Bacterial vaginosis (BV) is the most common vaginal infection in people of reproductive age. It happens when the balance of bacteria in the vagina shifts: the beneficial bacteria that normally dominate get crowded out by a mix of other bacteria that are usually present only in small numbers. BV is not a sexually transmitted infection, though sexual activity is one of the factors that can trigger it.
What Happens Inside the Vagina
A healthy vagina is home to large populations of Lactobacillus bacteria. These bacteria produce lactic acid, which keeps the vaginal environment slightly acidic (a pH below 4.5) and inhospitable to harmful organisms. In BV, Lactobacillus numbers drop sharply and get replaced by a surge of anaerobic bacteria, organisms that thrive in low-oxygen environments. The key players include Gardnerella vaginalis, Atopobium vaginae, Prevotella, Mobiluncus, and several others.
This isn’t a single “bug” causing an infection the way strep throat works. It’s a shift in an entire ecosystem. The overgrowth of anaerobic bacteria raises vaginal pH above 4.5, and the byproducts these bacteria produce are responsible for the symptoms most people notice.
Symptoms of BV
Many people with BV have no symptoms at all. When symptoms do appear, the most recognizable one is a fishy odor from vaginal discharge, often more noticeable after sex or during a period. The discharge itself tends to be thin, grayish, and heavier than usual, with a milklike consistency that coats the vaginal walls evenly.
BV can cause mild irritation, but it typically does not cause significant pain, burning, or itching. If you’re experiencing intense itching or a thick, lumpy discharge, that pattern points more toward a yeast infection than BV (more on that below).
BV vs. Yeast Infections
These two conditions get confused constantly because they both involve abnormal discharge. The differences are fairly distinct once you know what to look for:
- Discharge: BV produces thin, grayish discharge. Yeast infections produce thick, white, cottage cheese-like discharge.
- Odor: BV almost always comes with a fishy smell. Yeast infections usually have little to no odor.
- Pain and itching: Yeast infections cause noticeable itching, burning, and sometimes pain during sex. BV may cause mild irritation but rarely pain.
The treatments are completely different, so getting the right diagnosis matters. Over-the-counter antifungal creams treat yeast infections but do nothing for BV, which requires prescription antibiotics.
What Raises Your Risk
Researchers still don’t fully understand why BV develops. The condition occurs most often in people who are sexually active, but it can also happen in people who have never had sex. Several factors are known to increase risk:
Douching is one of the strongest. The vagina is self-cleaning, and rinsing it with water, vinegar, or commercial products disrupts the bacterial balance and can directly trigger the overgrowth of anaerobic bacteria. Having new or multiple sexual partners also increases risk, though the exact mechanism linking sex to BV remains unclear. Not using condoms and having a natural tendency to produce fewer Lactobacillus bacteria are additional risk factors. BV is also more common when both sexual partners are female.
How BV Is Diagnosed
A healthcare provider can usually diagnose BV during a standard pelvic exam using a set of clinical criteria. Diagnosis requires at least three of the following four findings: the characteristic thin, milklike discharge; a vaginal pH above 4.5; a fishy odor when a chemical solution is applied to a sample of discharge (sometimes called the “whiff test”); and the presence of “clue cells” under a microscope, which are vaginal cells covered in a visible coating of bacteria.
Lab-based scoring systems also exist. One widely used method, the Nugent score, grades a vaginal sample on a scale of 0 to 10 based on the types of bacteria visible under a microscope. A score of 7 to 10 confirms BV, while 0 to 3 indicates a healthy Lactobacillus-dominant environment.
Treatment and the Recurrence Problem
BV is treated with prescription antibiotics, either taken by mouth or applied as a vaginal gel or cream. Treatment courses are typically short, lasting five to seven days. Most people respond well to the initial round of antibiotics, and symptoms often improve within a few days.
The bigger challenge is recurrence. Within 6 to 12 months of finishing antibiotic therapy, 50% to 80% of people will experience BV again. This high recurrence rate is one of the most frustrating aspects of the condition. The anaerobic bacteria can form protective communities called biofilms on the vaginal wall, making them difficult to fully eliminate. When antibiotics are stopped, these bacteria can rebound and re-establish the imbalance.
For people dealing with frequent recurrence, providers may recommend extended or suppressive antibiotic regimens. Some research has explored whether probiotics or vaginal Lactobacillus supplements help prevent recurrence, but evidence on their effectiveness remains mixed.
Why Untreated BV Matters
BV is often dismissed as a nuisance, but leaving it untreated carries real health consequences. The disrupted vaginal environment makes it easier for sexually transmitted infections, including HIV, gonorrhea, and chlamydia, to take hold. BV also increases the risk of pelvic inflammatory disease, which can affect fertility.
During pregnancy, BV raises concerns about preterm delivery, or birth before 37 weeks. Preterm birth is linked to serious complications for newborns, including breathing problems and bleeding in the brain. The relationship between BV and preterm delivery is well documented, though researchers are still working to clarify whether BV directly causes early labor or is a marker for other contributing factors.
Reducing Your Risk
Because the exact cause of BV isn’t fully understood, prevention isn’t always straightforward. The steps with the strongest evidence behind them are practical: don’t douche, use condoms consistently, and limit the number of sexual partners. These measures help preserve the natural Lactobacillus populations that keep the vaginal environment stable. If you notice the telltale fishy odor or grayish discharge, getting tested sooner rather than later means faster treatment and a lower chance of complications.