What causes bacterial vaginosis?

Get from yourself: Bacterial vaginosis is a very common vaginal infection in women. It is from bacteria that live normally in the colon, but because the distance between the rectum and vagina is so short those bacteria can get into the vagina and cause an infection. Douching increases the chance of it. Symptoms include irritation, itching, odd discharge and fishy odor. I usually prescribe a vaginal antibiotic.

Unknown, complicated: BV is overgrowth of some vaginal bacteria and undergrowth of others. Most or all the bacteria are entirely normal in the vagina -- it's the change in numbers that's important. Why it happens isn't clear. In some ways, BV behaves like an STD -- uncommon in virgins, more frequent with new or multiple partners. But no known germ comes from male partners, and treating male partners doesn't prevent it.