The breast is a gland made up of connective and fatty tissues. There are small clusters of milk making cells in the back of the breast called alveoli. A hormone made in your pituitary gland called Prolactin causes your alveoli to take nutrients (proteins, sugars) from your blood supply and turn them into breast milk. Oxytocin causes the cells around the alveoli to contract and eject your milk down the milk ducts. This passing of the milk down the ducts is called the “let-down” (milk ejection) reflex. Most of us will have multiple let downs in a single feeding/pumping session but in general only feel the first one, which is the strongest.

Let down is usually triggered by stimulation of the nipple, either from baby’s mouth or a breast pump. Some people feel their let down like:
🔥Burning
📌Pins and needles
⚡️An electric shock
☀️Warmth

Some people never feel their let down. They know they’re in let down when:
🥛Leaking milk from the other breast
🤱🏽Baby audibly swallowing milk

Others may let down just fine for their baby and struggle to let down for their pump. The let-down reflex also may occur if a feeding is overdue, if you hear a baby cry, or if you think about your baby. You can teach yourselfg to let down by training your body to respond to a sound, smell, or event. You can also trigger more let downs when pumping by alternating between the stimulation and expression modes on the pump.