Bacterial vaginosis, commonly called BV, is the most common vaginal infection in women of reproductive age. It happens when the balance of bacteria in the vagina shifts, replacing the healthy bacteria that normally dominate with an overgrowth of other types. BV is not a sexually transmitted infection, though sexual activity can increase the risk of developing it.
What Happens Inside the Vagina During BV
A healthy vagina is home to a community of bacteria, and one group in particular does most of the heavy lifting. Lactobacillus bacteria produce lactic acid, which keeps the vaginal environment slightly acidic (a pH between 3.5 and 4.5). That acidity acts like a natural defense system. These bacteria also produce hydrogen peroxide and other antimicrobial compounds that prevent harmful organisms from gaining a foothold.
In BV, lactobacillus bacteria are dramatically depleted and replaced by a mix of anaerobic bacteria, organisms that thrive in low-oxygen environments. The exact trigger for this takeover is still unknown, but the consequences are clear: without lactobacillus keeping the environment acidic, vaginal pH rises and becomes more alkaline. That shift creates conditions where anaerobic bacteria multiply rapidly, and the protective ecosystem breaks down.
Common Symptoms
Many people with BV have no symptoms at all, which means it can go unnoticed for weeks or longer. When symptoms do appear, the most recognizable ones include:
- Discharge: A thin white or gray vaginal discharge, often with a noticeable fishy odor that gets stronger after sex
- Itching or burning: Pain, itching, or burning in or around the vagina
- Burning during urination
The fishy smell is one of the hallmarks that distinguishes BV from other vaginal infections. Yeast infections, by comparison, typically produce a thick, white, cottage cheese-like discharge without a strong odor. If you’re experiencing a thin, grayish discharge with a distinct smell, BV is the more likely culprit.
Risk Factors
BV is not caused by poor hygiene. In fact, overwashing or douching can disrupt the vaginal bacterial balance and increase your risk. Other factors associated with BV include having a new sexual partner or multiple partners, not using condoms, and using scented soaps or products in the vaginal area. BV is more common among women who have sex with women, likely because vaginal bacteria can be shared between partners.
Hormonal changes can also play a role. Shifts in estrogen levels during menstruation, pregnancy, or menopause can alter the vaginal environment enough to make BV more likely.
Why BV Matters Beyond Discomfort
Left untreated, BV is more than just an unpleasant nuisance. The disrupted vaginal environment makes you more vulnerable to sexually transmitted infections, including HIV, herpes, chlamydia, and gonorrhea. The loss of the protective acidic barrier essentially leaves the door open for other infections to take hold more easily.
During pregnancy, BV carries additional risks. It has been associated with preterm delivery, early miscarriage, postpartum uterine infections, and low birth weight. For this reason, pregnant women with symptoms are typically tested and treated promptly.
How BV Is Diagnosed
Diagnosis usually starts with a pelvic exam and a sample of vaginal discharge. Your provider may check the pH of the vagina, since BV raises it above the normal acidic range. They may also look at the discharge under a microscope. One common laboratory method scores the sample on a scale from 0 to 10 based on the types of bacteria visible: a score of 0 to 3 indicates a healthy, lactobacillus-dominant environment, 4 to 6 is considered intermediate, and 7 to 10 confirms BV.
A “whiff test” is sometimes used as well. Adding a drop of a chemical solution to the discharge sample releases a fishy odor when BV-associated bacteria are present.
Treatment
BV is treated with antibiotics, either taken by mouth or applied directly inside the vagina as a cream or gel. A typical course lasts about seven days. Both oral and topical options are effective, and your provider will help determine which makes the most sense for your situation.
Symptoms usually improve within a few days of starting treatment, but it’s important to complete the full course even if you feel better sooner. Stopping early can allow the anaerobic bacteria to bounce back before the healthy bacteria have fully re-established themselves.
You should avoid alcohol during oral antibiotic treatment and for at least 24 hours after finishing the course, as the combination can cause nausea and vomiting. If you’re using a vaginal cream, be aware that oil-based formulations can weaken latex condoms.
Recurrence Is Extremely Common
One of the most frustrating aspects of BV is how often it comes back. Between 50% and 80% of women experience a recurrence within 6 to 12 months of finishing antibiotic treatment. This high recurrence rate suggests that antibiotics clear the overgrown bacteria effectively in the short term but don’t always restore the underlying bacterial balance needed to prevent a relapse.
For women with frequent recurrences, extended or suppressive antibiotic therapy may be recommended, where a lower dose is used over a longer period to keep BV from returning. Some providers also discuss probiotic supplements aimed at replenishing vaginal lactobacillus, though the evidence on their effectiveness is still mixed and no specific probiotic regimen has been formally recommended as a standard treatment.
Reducing Your Risk
Because the exact cause of BV remains unclear, there’s no guaranteed way to prevent it. But several practices can help maintain a healthier vaginal environment. Avoid douching entirely, as it washes away protective bacteria. Use unscented soaps and avoid putting any fragranced products inside or around the vagina. Condoms during sex may reduce the risk by limiting the introduction of new bacteria.
Cotton underwear and breathable clothing can help keep the vaginal area dry, since excess moisture creates a more hospitable environment for anaerobic bacteria. After using the bathroom, wiping front to back prevents introducing bacteria from the rectal area. These are small adjustments, but for women prone to recurrent BV, they can make a meaningful difference in how often episodes occur.