Why is the human mouth so full of bacteria?

The human mouth is full of bacteria because the mouth is a warm, wet environment, and these are perfect conditions for bacteria to reproduce. Consider this: About 800 to 1,000 different types of bacteria may call your mouth “home.” Despite their tiny size, bacteria can do some big damage to your mouth. They do this by forming a sticky layer called plaque on your teeth, causing damage to your teeth and gums by releasing acids. These acids break down tooth enamel and can cause tooth decay. The bacteria in plaque can also foster swollen, painful gums. To prevent all these “side effects” of having bacteria in your mouth, remember to brush and floss daily and to visit your dentist regularly.