Increased levels of sex hormone-binding globulin
Estrogens can increase blood levels of the protein sex hormone-binding globulin (SHBG), which binds free testosterone (the active form) more strongly than estrogen, leading to decreased action of testosterone in male breast tissue. Conditions such as hyperthyroidism and chronic liver disease affect levels of SHBG, leading to symptomatic gynecomastia. Androgen resistance
Dysfunction in the androgen receptor prevents the effects of testosterone from acting on its target tissues. Androgen insensitivity syndromes result from the different degrees of resistance to the effects of androgens, and can cause external genitalia that may not be aligned with the genotype of the individuals sex chromosomes. Complete androgen insensitivity syndrome results in the failure to develop external genitalia such as the penis and scrotum along with development of breasts in an individual with testes. Partial androgen insensitivity syndrome may result in a variety of presentations. Minimal androgen insensitivity syndrome may present as gynecomastia in adolescence and may additionally be associated with infertility. Medications
Medications are known to cause gynecomastia through several different mechanisms. These mechanisms include increasing estrogen levels, mimicking estrogen, decreasing levels of testosterone or other androgens, blocking androgen receptors, increasing prolactin levels, or through unidentified means. Potential sources of estrogen include oral contraceptive pills, spironolactone, and anabolic steroids.High levels of prolactin in the blood (which may occur as a result of certain tumors or as a side effect of certain medications) has been associated with gynecomastia. A high level of prolactin in the blood can inhibit the release of gonadotropin-releasing hormone and therefore cause secondary hypogonadism.
Dimpling of the skin, nipple discharge, and nipple retraction are not typical features of gynecomastia and may be associated with other disorders. Milky discharge from the nipple is not a typical finding, but may be seen in a gynecomastic individual with a prolactin secreting tumor. An increase in the diameter of the areola and asymmetry of the chest are other possible signs of gynecomastia.Gynecomastia has psychosocial implications that may be particularly challenging for adolescents who are experiencing physical maturation and self-identity formation, which includes body image disturbances, negative attitudes towards eating, self-esteem problems, social withdrawal, anxiety, and shame. Men with gynecomastia may appear anxious or stressed due to concerns about its appearance and the possibility of having breast cancer. Causes
Gynecomastia is thought to be caused by an altered ratio of estrogens to androgens mediated by an increase in estrogen action, a decrease in androgen action, or a combination of these two factors. Estrogen and androgens have opposing actions on breast tissue: estrogens stimulate proliferation while androgens inhibit proliferation. The cause of gynecomastia is unknown in around 25% of cases. Known causes can be physiologic (occurring normally) or non-physiologic due to underlying pathologies such as drug use, chronic disease, tumors, or malnutrition. Physiologic
Physiologic or normal gynecomastia can occur at three timepoints in life: shortly after birth in both female and male infants, during puberty in adolescent males, and in older adults over the age of 60. Newborns
60-90% of male and female newborns may show breast development at birth or in the first weeks of life.