Physiologic gynecomastia occurs in neonates, at or before puberty and with aging . Many cases of gynecomastia are idiopathic, meaning they have no clear cause.
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.
Medications cause 10-20% of cases of gynecomastia in post-adolescent adults. These include cimetidine, omeprazole, spironolactone, imatinib mesylate, finasteride and certain antipsychotics.
Some act directly on the breast tissue, while others lead to increased secretion of prolactin from the pituitary by blocking the actions of dopamine (prolactin-inhibiting factor/PIF) on the lactotrope cell groups in the anterior pituitary.
Androstenedione, used as a performance enhancing food supplement, can lead to breast enlargement by excess estrogen activity. Medications used in the treatment of prostate cancer , such as antiandrogens and GnRH analogs can also cause gynecomastia.
Marijuana use is also thought by some to be a possible cause; however, published data is contradictory.
Increased estrogen levels can also occur in certain testicular tumors , and in hyperthyroidism . Certain adrenal tumors cause elevated levels of androstenedione which is converted by the enzyme aromatase into estrone, a form of estrogen.
Other tumors that secrete hCG can increase estrogen. A decrease in estrogen clearance can occur in liver disease, and this may be the mechanism of gynecomastia in liver cirrhosis . Obesity tends to increase estrogen levels.
Decreased testosterone production can occur in congenital or acquired testicular failure, for example in genetic disorders such as Klinefelter Syndrome . Diseases of the hypothalamus or pituitary can also lead to low testosterone.
Abuse of anabolic androgenic steroids (AAS) has a similar effect. Mutations to androgen receptors, such as those found in Kennedy disease can also cause gynecomastia.
Although stopping these medications can lead to regression of the gynecomastia, surgery is sometimes necessary to eliminate the condition.
Repeated topical application of products containing lavender and tea tree oils among other unidentified ingredients to three prepubescent males coincided with gynecomastia; it has been theorised that this could be due to their estrogenic and antiandrogenic activity.
However, other circumstances around the study are not clear, and the sample size was insignificant so serious scientific conclusions cannot be drawn.