The vagina is a naturally acidic organ, and this is how it keeps bad bacteria and infections at bay. When the vagina is in a healthy, acidic state, the environment is too harsh for bad bacteria to grow. These bacteria need higher pH levels (less acidic) to thrive.
However, when outside factors shift a vagina from acidic to alkaline, an overgrowth of bad bacteria can occur. This brings discharge, bad odor, itching and other unpleasant stuff.