Tooth decay is caused by the loss of hard tissue from the enamel and dentin of the tooth. For decay to occur three factors must be present in the mouth at the same time: the tooth, bacteria, and carbohydrates. The bacteria that are normally present in the mouth eat the carbohydrates and produce acid. This acid then dissolves the enamel of the tooth.

When carbohydrates and bacteria are absent from the mouth, acid is not produced and can actually heal teeth. Cavities are formed when the destruction of enamel is greater than the rate of healing. A cavity is a hole in the tooth caused by decay. Fluoride, toothpaste, and certain foods can help heal teeth and prevent cavities from forming.

Dental erosion, another form of tooth decay, is the loss of enamel on the tooth surface from acidic food or drinks. When the acidic food or liquid constantly washes over the tooth, it dissolves the enamel over time. The acidity of food and beverages can be measured using the pH scale. Anything below a 7 is considered acidic and the lower the number the more acidic it is. For example, tomato juice has a pH of 4.1 and a can of Coke has a pH of 2.47 making Coke more acidic than tomato juice.