Bacterial vaginosis is an infection of the vulva and vagina. It is associated with an imbalance of bacteria in the vagina.

Vagina
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A mix of good and bad bacteria are normally found in the vagina. Bacterial vaginosis occurs when there is an increase in the amount of bad bacteria. The increased bad bacteria causes a decrease in good bacteria. This imbalance can lead to symptoms.

It is not clear exactly what causes the increase in bad bacteria.