Pediatrics (also spelled paediatrics or pædiatrics) is the branch of medicine that involves the medical care of infants, children, and adolescents. The American Academy of Pediatrics recommends people be under pediatric care up to the age of 21. A medical doctor who specializes in this area is known as a pediatrician, or paediatrician. The word pediatrics and its cognates mean "healer of children"; they derive from two Greek words: παῖς (pais "child") and ἰατρός (iatros "doctor, healer"). Pediatricians work both in hospitals, particularly those working in its subspecialties such as neonatology, and as primary care physicians.