gynecomastia

Gynecomastia is the growth of true breast (glandular) tissue in a male. It reflects a tug-of-war between hormones gone slightly off balance: estrogen, which stimulates breast tissue, gaining the upper hand over androgens, which oppose it.

The underlying cause is a relative increase in estrogen action compared with androgen action in the breast. This can come from too much estrogen (for instance from extra aromatase activity in obesity, certain tumors, or liver disease that slows hormone clearance), too little androgen (hypogonadism), or drugs that either add estrogen-like activity or block androgens. It is real glandular tissue, which distinguishes it from the soft fatty enlargement of pseudogynecomastia seen with simple weight gain.

Importantly, gynecomastia is often physiological and benign. It appears commonly in newborns from maternal estrogen, in many boys at puberty due to a transient estrogen-androgen mismatch (usually resolving on its own), and in older men as testosterone falls. Persistent, painful, or rapidly growing or one-sided breast tissue warrants evaluation, since it can occasionally signal a hormone-secreting tumor or, rarely, male breast cancer.