"The acid attacks enamel." Enamel is

Tooth decay begins with bacteria. The bacteria in the mouth feed on the sugars and starches in food and drink and turn them into acid. The acid attacks enamel, the hard outer surface of the tooth.

Each attack takes some minerals out of the enamel. At first this shows as white spots. At this early stage the damage can be stopped or even reversed, because enamel can repair itself with minerals from saliva and from fluoride. If the attacks go on, the enamel is worn through and a hole, called a cavity, forms, which a dentist has to fill.

Early decay usually causes no pain, so many people do not know they have it. As it gets worse it can cause toothache, or make the teeth sensitive to sweet, hot or cold food. An infected tooth can form an abscess, causing pain, a swollen face and fever.

Decay can be prevented. Brush twice a day with a fluoride toothpaste and clean between the teeth with floss. Drink fluoridated tap water where it is available. Cut down on sugary drinks and on foods full of sugar and starch, and snack less often. Dentists can also coat the chewing surfaces of the back teeth with thin protective sealants.