Cause

Bacterial vaginosis is caused by an imbalance of the organisms (flora) that naturally exist in the vagina. Normally, about 95% of vaginal flora are lactobacillus bacteria. (These types are unique to humans, different from the lactobacillus in yogurt.) These lactobacilli help keep the vaginal pH level low and prevent overgrowth of other types of organisms. Women with bacterial vaginosis have fewer lactobacillus organisms than normal and more of other types of bacteria. Experts do not yet understand what causes this imbalance.

Although the specific cause isn't known, a number of health and lifestyle factors have been linked to bacterial vaginosis. For more information, see the What Increases Your Risk section of this topic.

Symptoms

Many women with bacterial vaginosis do not have any symptoms. Bacterial vaginosis does not typically cause itching. But it does cause:

• An excessive grayish white vaginal discharge, unlike normal vaginal discharge (1 out of 3 women who have bacterial vaginosis describe the discharge as yellow).¹
• A bothersome "fishy" odor, which is usually worse after sex (intercourse).

Other conditions with similar symptoms include some sexually transmitted infections (especially trichomoniasis), urinary tract infection, and vaginal yeast infection.