Bacterial vaginosis (BV) is a vaginal infection caused by an imbalance of “good” and “harmful” bacteria.

It’s normal for a woman to have bacteria in her vagina. Most of the bacteria, called lactobacilli, are beneficial. Other types of bacterial (anaerobes) are considered harmful, but as long as they don’t outnumber the good bacteria, there usually isn’t a problem.

BV develops when there is more harmful bacteria than good bacteria. Experts aren’t sure how this imbalance happens.

Most women with BV don’t have any symptoms. Those who do may have a white or gray vaginal discharge with a distinct odor, sometimes described as “fishy.” Burning during urination and itching outside the vagina are other symptoms.

While the exact cause of BV isn’t known, certain behaviors increase the risk:

• Sex partners. Women who have many partners are more susceptible to BV, as are women who have a new sex partner. BV also tends to be more common among women who have sex with women.

• Douching. Some women douche – or cleanse the vagina – regularly. This can spur the growth of anaerobes, disrupting the balance of good and harmful bacteria.

The first step in diagnosing BV is a pelvic exam. A doctor can test vaginal secretions to see whether the harmful bacteria outnumber the good. Sometimes, a doctor will test the acidity in the vagina with a pH strip. BV is a possibility if the vaginal pH measurement is 4.5 of higher.

BV can be treated with medication. Women should not try to treat the infection themselves. BV has a number of complications, including greater risk of getting a sexually-transmitted infection and higher rates of infection during surgical procedures, like a hysterectomy or abortion. Pregnant women with BV are at higher risk for preterm delivery and having a low birth weight baby.