There are many hormones related to milk secretion. After pregnancy, the placenta secretes a large amount of estrogen, which promotes the development of the mammary gland ducts, and progesterone, which is useful for the development of the glandular vesicles. Prolactin, which is secreted by the pituitary gland, placenta, lactogen, cortisol, etc., all play a role in the development of the mammary glands and the secretion of milk. After the birth of a baby, the secretion of prolactin will increase, and the secretion of milk will increase under the stimulation of the baby. Through the baby’s sucking, it can reflexively tell the pituitary gland to secrete more milk, and the pituitary gland will in turn secrete more prolactin. Through continuous stimulation, the mother will have more and more milk, and sucking is also the best way to promote milk secretion.