Answer: When your baby suckles, it sends a message to your brain. The brain then signals the hormones, prolactin and oxytocin to be released. Prolactin causes the alveoli to begin making milk. Oxytocin causes muscles around the alveoli to squeeze milk out through the milk ducts.
Milk production occurs within the alveoli, which are grape-like clusters of cells within the breast. Once the milk is made, it is squeezed out through the alveoli into the milk ducts, which resemble highways. Women with small breasts make the same quantity and quality of milk as women with larger breasts.