Milk in the breast is produced by stimulating the secretion of milk from the mammary gland follicles through lactogen, and then through oxytocin, which causes the milk to be discharged through the ducts, creating the milk ejection reflex. Once a woman enters pregnancy, her mammary glands are stimulated by estrogen and progesterone to develop rapidly. When entering the second trimester of pregnancy and breastfeeding, the mother’s body will secrete lactogen and oxytocin, which can act on the mammary gland follicles to stimulate the secretion of milk from the mammary gland follicles, and the baby’s sucking will stimulate the hypothalamus in a positive feedback manner, producing more lactogen, and the amount of milk will also increase. Oxytocin, on the other hand, promotes the contraction of the smooth muscle of the mammary glands, causing the milk present in the alveoli to be discharged through the ducts, forming the milk spurt reflex, so that the baby can suckle on the milk.