The most common cause of gynecomastia in the male is puberty. 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, is self-limiting, 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 and in rare cases may persist until the child is two years old. It is caused by exposure to maternal hormones. Other causes of gynecomastia include decreased production of testosterone, chronic liver disease, kidney failure,exposure to estrogens or androgens (often taken secretly for body building), marijuana use, and some medications (such as eplerenone (Inspra), ACE-inhibitors, and phenytoin (Dilantin)). Rare causes include tumors, genetic defects, or an overactive thyroid.
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