Gynecomastia (American English) or gynaecomastia (British English) is the development of abnormally large breasts on males. The term comes from the Greek gyne meaning "woman" and mastos meaning "breast". The condition can occur physiologically in neonates, in adolescents, and in the elderly. In adolescent boys the condition is often a source of distress, but for the large majority of boys whose pubertal 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 either breast tissue or pectoral adipose tissue, and often a combination of the two. Breast prominence due solely to excessive adipose is often termed pseudogynecomastia
Physiologic gynecomastia occurs in neonates, at puberty and with aging.
Potential pathologic causes of gynecomastia are: medications including hormones, increased serum estrogen, decreased testosterone production, androgen receptor defects, chronic kidney disease, chronic liver disease, HIV, and other chronic illness. Gynecomastia as a result of spinal cord injury and refeeding after starvation has been reported. In 25% of cases, the cause of the gynecomastia is not known.
