Which hormone triggers lactation after childbirth?

Prolactin is the hormone that triggers lactation after childbirth. It is produced by the anterior pituitary gland and plays a crucial role in the initiation and maintenance of milk production in response to the infant suckling. After delivery, there is a dramatic drop in estrogen and progesterone levels, which were high during pregnancy, allowing prolactin to take effect without inhibition. The suckling of the infant stimulates the nerve receptors in the nipple, leading to the release of prolactin. This ensures that milk is produced to feed the newborn.

While oxytocin, another important hormone involved in the breastfeeding process, is responsible for milk ejection or let-down reflex, it is not responsible for initiating lactation itself. Estrogen and progesterone primarily prepare the breasts for lactation during pregnancy but do not trigger the actual milk production post-delivery. Thus, prolactin is recognized as the key hormone for establishing lactation following childbirth.