Bacterial vaginosis is caused by a change in the normal bacterial flora of the vagina and causes a decrease in hydrogen peroxide-producing lactobacilli and overgrowth, mainly of anaerobic bacteria. Bacterial vaginosis is the most common form of vaginitis in the United States. In the normal vaginal flora, anaerobic bacteria are less than 1% while in women with bacterial vaginosis; anaerobes and Gardnerella vaginalis and Mycoplasma hominis are 100 to 1000 times more than normal and lactobacilli are usually absent, in which case restoration of normal vaginal flora is difficult and recurrence of bacterial vaginosis is common. The diagnosis of bacterial vaginosis is based on the following findings:

Gray vaginal discharge with a fishy odor that is particularly noticeable after intercourse with a pH above 4.5 (usually 4.7 to 5.7), an increase in the number of clue cells, and an obvious lack of white blood cells in the vaginal discharge microscopy (in advanced cases of bacterial vaginosis, more than 20% of epithelial cells are clue cells.) Also, inhaling the smell of fish, similar to amines after adding KOH to vaginal secretions (whiff test). Failure to treat of bacterial vaginosis has many consequences, including an increased risk of pelvic inflammatory disease. Metronidazole, which is used to treat this disease, is associated with side effects such as nausea, metallic taste in the mouth, peripheral neuropathy, and Candida infection.

The use of herbal medicine in vaginal infections has a long history. In alternative medicine, marjoram and lemon balm have been used to treat bacterial vaginosis.