Breastfeeing is the feeding of an infant or young child with milk from a woman's breasts. Babies have a sucking reflex that enables them to suck and swallow milk. With few exceptions, human breast milk is the best source of nourishment for human infants. There are circumstances under which breastfeeding can be difficult, however, or even in rare instances contraindicated. This article looks at some of the complications that can arise in breastfeeding.