Gynecomastia (guy-nuh-koh-MAS-tee-uh) is an increase in the amount of breast gland tissue in boys or men. An imbalance of the hormones estrogen and testosterone causes it. Gynecomastia can affect one or both breasts, sometimes unevenly.
Pseudogynecomastia is an increase in fat but not gland tissue in male breasts. Newborns, boys going through puberty and older men may develop gynecomastia due to natural changes in hormone levels. There are other causes too.
Most often, gynecomastia isn't a serious problem. But it can be tough to cope with the condition. People with gynecomastia sometimes have pain in their breasts. And they may feel embarrassed.