Gynecomastia is a noncancerous enlargement of one or both breasts in men or boys. It is often due to an excess of the female hormone estrogen (which is also produced naturally in males, but normally only in small amounts).
Mild, temporary gynecomastia can occur at birth as a result of maternal hormones, and is also common at puberty.
Gynecomastia in later life may be a result of being overweight, due to increased estrogen produced by fat cells.
Adult gynecomastia may also be due to some medications, long-term liver disease, or a hormone-secreting testicular or pituitary tumor.
Treatment depends on the cause. If there is no underlying disorder, the excess breast tissue may be removed surgically.