How Your Breasts Produce Milk
Milk is produced in the glandular tissue (alveoli) of the breasts. The smooth muscle tissue around each tiny milk-producing cell contracts when maternal hormones are released. This contraction propels milk down the milk ducts to the openings in the nipple. This process is called the milk ejection reflex or the letdown. Your baby's cry and touch, nipple stimulation, and sucking all can trigger this hormone release. The majority of milk obtained during breastfeeding, hand expression, or breast pumping occurs during milk ejections, each of which last about 1-2 minutes. Multiple letdowns appear to occur during most breastfeeding sessions.
When the milk is actively ejecting, many women will notice a bit of tingling, especially during the first letdown of the feeding. The other letdowns may be less intense. The breastfeeding mother may simply notice the baby begin to gulp again after seeming to rest at the breast for a few minutes. A mother who is pumping may notice more milk sprays or an increase in the milk flow. When pumping, it is important to ensure that you pump long enough to trigger several letdowns.