There are billions of bacteria in one little chunk of plaque.
Normally, the good bacteria balance the bad to form a healthy, odor-free ecosystem in your mouth. Your baby breath turns rancid when anaerobes overrun the system. These bacteria, which flourish in the absence of oxygen, usually live at the back of the tongue, where they are partially protected from oxygen and spit by a film of food, dead cells and mucus. Another source of stench is plaque, which your dentist has probably been lecturing you about since grade school. Eating too many sweets and failing to brush can cause plaque buildup on your teeth, which may spread into the pockets of your gums. Here the bacteria in plaque can cause not only gum disease, but terrible breath.