Gynecomastia is the development of abnormally large mammary glands in males resulting in breast enlargement. The condition can occur physiologically in neonates, in adolescence, and in the elderly. In adolescent boys the condition is often a source of distress, but for the large majority of boys whose pubescent gynecomastia is not due to obesity, the breast development shrinks or disappears within a couple of years.
The causes of common gynecomastia remain uncertain, although it has generally been attributed to an imbalance of sex hormones or the tissue responsiveness to them; a root cause is rarely determined for individual cases. Breast prominence can result from hypertrophy of breast tissue, chest adipose tissue and skin, and is typically a combination.