Cavities are permanently damaged areas in the hard surface of your teeth that develop into tiny openings or holes. Cavities, also called tooth decay or caries, are caused by a combination of factors, including bacteria in your mouth, frequent snacking, sipping sugary drinks and not cleaning your teeth well.Cavities and tooth decay are among the world’s most common health problems. They’re especially common in children, teenagers and older adults. But anyone who has teeth can get cavities, including infants.