Cavities are small holes that slowly develop in the teeth. They are caused by tooth decay.
Tooth decay is damage to a tooth caused by bacteria in your mouth (plaque). These bacteria make acids that can eat away at the hard outer layer (enamel) of the tooth.
Mild tooth decay may be helped with effective tooth-brushing and flossing. Daily rinsing with fluoride mouth care products can help. More serious tooth decay may need fillings. This can stop the decay and prevent further damage to the tooth.
Babies can get cavities too. It's called "baby bottle tooth decay." This can happen when babies are put to bed with a bottle or are allowed to keep sucking on a bottle with any drink that has sugar in it, such as juice. Cavities in babies can often be prevented by cleaning their mouth and teeth after their last feeding before bed.