One of the hallmarks of BV is the absence of a specific type of bacteria that defines the healthy vagina: certain species of lactobacillus (sometimes also called lactobacilli). The lactobacilli found in the healthy vagina are generally found only in humans (meaning you can’t get them by eating or douching with dairy products, like yogurt!) and often produce chemicals that act like antibiotics to fend off foreign invaders, including STDs like chlamydia and gonorrhea. One of these chemicals is hydrogen peroxide.
In BV, the normally robust population of vaginal lactobacilli essentially disappear, for reasons that are not completely understood, and are replaced by large numbers of bacteria that characterize BV, including Gardnerella vaginalis. While we think that some behaviors probably increase a woman’s risk of BV, including douching (which probably reduces the good lactobacilli if it’s done frequently) and unprotected sex (sometimes with a specific partner, and especially between female sex partners), we don’t really know what causes BV.
The best way to avoid getting BV is to avoid douching, use precautions to increase sexual safety as you would to protect yourself against any STD, and to seek care if you notice abnormal vaginal discharge or an unusual genital odor. BV usually responds well to antibiotic therapy, which can be given as oral medication (pills) or vaginal gel or cream for 5-7 days; however, many women will experience a repeat episode, and some might need to go on long-term suppressive therapy (usually vaginal antibiotic gel twice a week) to keep it at bay.
–Jeanne Marrazzo, MD, MPH