Gynecomastia is the growth of abnormally large breasts in males. It is due to the excess growth of breast tissue, not excess fat tissue.
Breast development in a male
The condition may occur in one or both breasts and begins as a small lump beneath the nipple, which may be tender. The breasts often enlarge unevenly. Gynecomastia during puberty is not uncommon and usually goes away over a period of months.
In newborns, breast development may be associated with milk flow (galactorrhea). This condition usually lasts for a couple of weeks, but in rare cases may last until the child is 2 years old.
Androgens are hormones that create male characteristics, such as hair growth, muscle size, and a deep voice. Estrogens are hormones that create female characteristics. All men have both androgens and estrogens.
Changes in the levels of these hormones, or in how the body uses or responds to these hormones can cause enlarged breasts in men.
More than half of boys develop gynecomastia during puberty.
Ali O, Donohue PA. Gynecomastia. In: Kliegman RM, Stanton BF, Geme JW, Schor NF, Behrman RE, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 579.
Nancy J. Rennert, MD, Chief of Endocrinology & Diabetes, Norwalk Hospital, Associate Clinical Professor of Medicine, Yale University School of Medicine, New Haven, CT. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.