Introduction Types milk (galactorrhea) physical stimulation of nipple e.g. sexual intercourse ↑ prolactin e.g. prolactinoma primary hypothyroidism secondary to ↑ thyrotropin-releasing factor (TRF) TRF acts to ↑ prolactin drugs often bilateral greenish/brown mammary duct ectasia purulent acute mastitis bloody ductal cancer (older women) intraductal papilloma (young women)