A few days after birth, a newborn may have a bulge at the breast and may even have milk-like fluid coming out. Breast enlargement and lactation in newborns is a physiological phenomenon and does not require special treatment. Both male and female infants may experience breast lactation or enlargement within the first few days of life. This is caused by the fetus being exposed to high levels of hormones in the mother’s blood, such as lactogen, which cause the breast to enlarge. After birth, because maternal hormones remain in the newborn’s body for some time, the newborn’s breasts are swollen and can even produce milk. About 1 to 2 weeks after birth, the hormone level in the newborn’s body gradually decreases, and finally all the hormones are secreted and excreted, and the swollen breast phenomenon disappears automatically.