Gynecomastia is an abnormal enlargement of one or both breasts in men. Milk production may or may not be present.

Gynecomastia is fairly common. It is a physiologic phenomenon that occurs during puberty, when at least half of males experience enlargement of one or both breasts. Pubertal hypertrophy is characterized by a tender discoid enlargement of the breast tissue beneath the areola and usually subsides spontaneously within a year.

Gynecomastia also is common among elderly men, particularly...