Let-down occurs in response to the baby's suckling, though it also may be a conditioned response, e.g. Lactation can also be induced by a combination of physical and psychological stimulation, by drugs or by a combination of these methods.
Breastfeeding triggers biochemical reactions which allows for the enzymes, hormones, growth factors and immunologic substances to effectively defend against infectious diseases for the infant.
The breastmilk also has long-chain polyunsaturated fatty acids which help with normal retinal and neural development.
The first type, produced during the first days after childbirth, is called colostrum.
Benefits for the mother include less blood loss following delivery, better uterus shrinkage, weight loss, and less postpartum depression.
Breastfeeding delays the return of menstruation and fertility, a phenomenon known as lactational amenorrhea.