Breastmilk is made in small clusters of glands in your breasts called alveoli.
When your baby starts to suck, a hormone is released that signals your breasts to make milk.
Another hormone causes the alveoli to contract, which moves the milk into ducts that carry it to your nipples.
As the flow of milk begins, you may feel a tingling feeling in your breasts. This is called the "let-down reflex".