BV stands for bacterial vaginosis, the most common vaginal infection in women of reproductive age. It happens when the balance of bacteria inside the vagina shifts: protective bacteria decline, and other types of bacteria multiply in their place. BV is not a sexually transmitted infection, though sexual activity is one of the factors that can trigger it.
What Happens Inside the Vagina During BV
A healthy vagina is home to large numbers of a type of bacteria called Lactobacillus. These bacteria produce antimicrobial compounds that keep the vaginal environment slightly acidic, which prevents other organisms from growing out of control. When Lactobacillus numbers drop sharply, other bacteria that thrive in low-oxygen environments take over. The most common of these is Gardnerella vaginalis.
This bacterial shift raises the vagina’s pH above 4.5 (its normal range is around 3.8 to 4.5), creating an environment where harmful bacteria can continue multiplying. The result is the symptoms most people associate with BV: unusual discharge and a distinct odor.
How BV Feels and What to Look For
Many people with BV have no symptoms at all. When symptoms do show up, the most recognizable ones are:
- Discharge: Thin, off-white, gray, or greenish in color with a milklike consistency that coats the vaginal walls
- Odor: A fishy smell, often stronger after sex or during a period
- Irritation: Some people notice mild itching or burning, though this is less common than with yeast infections
BV does not typically cause significant pain, swelling, or thick, clumpy discharge. If you’re experiencing those symptoms, a yeast infection or another condition may be more likely.
What Increases Your Risk
BV rarely occurs in people who have never had sex, but researchers still don’t fully understand why sex contributes to it. It is not passed between partners the way a traditional STI is, yet sexual activity clearly plays a role. Having new or multiple sexual partners and not using condoms both increase the likelihood of developing BV.
Douching is another well-established risk factor. It disrupts the vaginal bacterial balance by washing away Lactobacillus and introducing outside substances. Beyond that, anything that alters vaginal pH, from scented soaps to certain menstrual products, can contribute.
How BV Is Diagnosed
A healthcare provider can diagnose BV during a routine exam. The standard clinical method checks for at least three of four signs: the characteristic thin discharge, a vaginal pH above 4.5, a fishy odor when a chemical solution is applied to a discharge sample, and the presence of “clue cells” (vaginal cells coated in bacteria) under a microscope. In some cases, your provider may send a swab to a lab for further testing instead.
Treatment and Why BV Often Comes Back
BV is treated with prescription antibiotics, available as either oral pills or a vaginal gel or cream. Treatment courses are short, typically lasting five to seven days. Most people see symptoms resolve within a few days of starting treatment.
The bigger challenge with BV is recurrence. Between 50% and 80% of women who complete antibiotic treatment will have BV come back within 6 to 12 months. This high recurrence rate is one of the most frustrating aspects of the condition. The antibiotics clear the overgrown bacteria, but they don’t always allow Lactobacillus to fully reestablish itself. Some providers recommend extended or suppressive antibiotic regimens for people dealing with frequent recurrences.
Why BV Matters During Pregnancy
For most people, BV is more of an annoyance than a serious health threat. During pregnancy, however, the stakes are higher. Research comparing pregnant women with and without BV found that preterm birth before 34 weeks occurred in 22.7% of those with BV, compared to 6.2% of those without it. Babies born to mothers with BV also had significantly lower birth weights on average (about 2,450 grams versus 2,950 grams) and were more than twice as likely to need intensive care after delivery.
BV during pregnancy is also linked to chorioamnionitis, an infection of the membranes surrounding the baby, which was found in more than half of pregnant women with BV in one study. Because of these risks, pregnant women who develop symptoms are typically screened and treated promptly.
Outside of pregnancy, untreated BV can also increase susceptibility to sexually transmitted infections, including HIV, and may raise the risk of pelvic inflammatory disease.
Reducing Your Risk of BV
There is no guaranteed way to prevent BV, but a few habits lower the odds. Avoiding douching is the single most impactful step, since it directly disrupts the vaginal microbiome. Using condoms during sex, limiting the number of sexual partners, and avoiding scented products in or around the vagina all help maintain a healthy bacterial balance. Some people find that probiotic supplements or foods support Lactobacillus levels, though the evidence for this as a standalone prevention strategy is still limited.
If you notice a change in your discharge or a new fishy odor, getting evaluated sooner rather than later means a shorter course of treatment and less time for the bacterial imbalance to become entrenched.