What is Gynecomastia?? Gynecomastia (pronounced: GUY-nuh-ko-MASS-tee-uh), which is also known as "man b---s" is a real medical condition which causes breast enlargement in men. The abnormal enlargement can be in both breasts or one, and sometimes milk will even be secreted. Technically, the condition results from the development of abnormally large mammary glands, and is more commonly seen in adolescent boys and elderly men.