Although gynecomastia, a phenomenon suffered by one out of every 5 men, is mostly seen in adolescents and middle-aged individuals, in some cases it can also be seen in newborn boys. The reason for this is the high amount of estrogen hormone passed from mother to baby during pregnancy; this situation may disappear spontaneously over time.
In adolescents, hormonal changes are the reason for the growth of breast tissue. During this period, while the testosterone level decreases, the estrogen level rises. Like the congenital gynecomastia problem, breast growth during puberty may lose its effect as one grows older.