When food is consumed, cariogenic bacteria, including Streptococcus mutans and Streptococcus sobrinus, are able to break down carbohydrates in the mouth, producing acids that cause mineral loss from teeth. These bacteria cling to teeth and live in colonies called plaque, a sticky collection of food substances and bacteria adhering to the teeth.

Sucrose has been more strongly associated with caries formation than any other carbohydrate. However, fermentable carbohydrates also include complex carbohydrates—bread, pasta, cereal, etc—that can be broken down to sugars in the oral cavity, as well as fruit juices. Bacterial metabolism of carbohydrates results in acid production.

The breakdown of enamel occurs slowly. The first signs are areas of demineralization that appear as white spots near the gum line. If the process continues, it leads to frank cavitation.