Are cavities contagious?

Yes, the bacteria that cause cavities (mutans streptococci) can pass between people through saliva. A baby is born without cavity-causing bacteria and usually acquires them from a caregiver, and the period from about 6 months to 3 years of age, when the baby teeth come in, is when the bacteria most easily take hold. Avoid sharing spoons and cups, blowing on food to cool it, and kissing on the mouth; treating the caregiver's own cavities first also helps prevent cavities in the child.