Education Bacterial vaginosis Bacterial vaginosis is caused by the overgrowth of bacteria present in your vagina. Generally, "good" bacteria (lactobacillus) are more than "bad" bacteria (anaerobic) in your vagina, but if anaerobic bacteria are very high, then they spoil the balance of bacteria, which causes bacterial vaginosis. This type of Vaginitis is related to sexual intercourse, especially if you have relationships with many people or when you are related to a new person. But it happens in women who are not sexually active.