Pediatrics 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 through the age of 21. In the United Kingdom, paediatrics covers patients until age 18. Worldwide age limits of pediatrics have been trending up year over year. 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 and ἰατρός. Pediatricians work in hospitals and children's hospitals particularly those working in its subspecialties, and as outpatient primary care physicians.