Infection- Sometimes an infection can cause the nipple. Your doctor can take a sample of the fluid discharge, and send it to a laboratory for testing. If an infection is found, you may need to take antibiotics to clear it.
Mastitis- If you are breastfeeding and becomes a clogged milk duct may cause mastitis. Milk collects behind a clogged duct, causing swelling and pressure. This can lead to infections, how bacteria can grow in the milk trapped. Your chest can turn pink and may feel tender and lumpy. You could see pus discharge from your nipple. Consult your doctor if you think the mastitis could be your problem.
Lumpy and dense texture Breast- If the breast tissue is dense and usually lumpy (cysts, fibroadenomas) you can see sticky nipple discharge green or brown.
Intraductal depigmented- A small wart as growth in the breast tissue can sometimes puncture a duct. Do not be alarmed – these depigmented carcinomas are common in premenopausal women and can occur in groups. Intraductal depigmented can be removed surgically, if they become bothersome.
Pregnancy- During pregnancy, breast tissue is maturing and preparing for breastfeeding. You can see clear or milky discharge (colostrum), which is normal.Mammary duct Ectasia- In some women approaching menopause, milk ducts can become swollen and clogged. These ducts are just below the nipple and the swelling can cause the nipple to feel tender or irritated and nipple. Mammary duct ectasia may cause gray and green discharge that is thick and sticky. You can get relief from this condition by using hot packs, but if the problem persists, consult your doctor. If your ducts are infected, you may need to take antibiotics. In cases when the learned shall not return to normal size, can be surgically removed, without causing a major change in the appearance of your chest.
other causes of nipple benign: A thyroid malfunction can cause Milky nipple. Clothing scratchy or Bras which do not fall, constantly rubbing or compressed your chest, can also cause the nipple. A breast abscess, usually below areola, may cause the nipple, signaling a bacterial infection. source: National Cancer Institute. Information on changes in the breast: A health guide for women. PDF File. August 2004.