The exact cause of bacterial vaginosis is unknown. There could be a variety of causes. No single organism causes it. It is a condition in which the natural balance of organisms found in the vagina changes. The healthy vagina normally contains a variety of bacteria. One kind of bacteria, known as lactobacillus, is particularly important. Lactobacilli keep the vagina slightly acidic to help reduce the growth of potentially harmful organisms. People who have bacterial vaginosis lose this protection and have both a large increase in the number of potentially harmful bacteria and a large decrease in the numbers of normal, protective lactobacilli in their vagina. This change in numbers and kinds of bacteria is believed to be the cause of bacterial vaginosis.

Nearly half of all people with bacterial vaginosis will experience no symptoms at all. When someone does have symptoms, the most common complaint is a foul or "fishy" smelling vaginal odor. This odor frequently increases following intercourse. In a recent survey of medical providers, more than half said that the most common complaint from people with bacterial vaginosis is vaginal odor. Another common symptom is an excessive white or gray discharge with a milk-like consistency that can stain undergarments.

Your medical provider may prescribe a medicine you can use vaginally for a prescribed length of time. Sometimes bacterial vaginosis is treated with oral medications. It is important to take the medicine as directed and to abstain from sexual contact until the treatment is completed.

Since bacterial vaginosis is not thought to be caused by sexual intercourse, most medical providers will not treat your sexual partner. If your infection should return, your medical provider may recommend treating your partner.