Nipple changes or discharge

Like the rest of the breast, your nipples can change over time and that's totally normal. What may not be normal is if you notice sudden changes in your nipples such as pain, retraction (where the nipple turns inward), or discharge that isn't breastmilk. This is because breast cancer often begins in milk-producing ducts and so nipples may be affected more noticeably than other parts of the  breast. 

An important note on retraction: inverted nipples can be totally normal in some women. It should only be cause for concern if one of your nipples that is normally extended, suddenly inverts. Similarly, while nipple discharge may be related to something completely different and benign, if you have a lump in your breast and also experience some sort of discharge, especially discharge that happens on its own (spontaneously) and is either clear or bloody, you should talk to your doctor immediately. 

There is also a rare form of breast cancer, known as Paget disease, that affects the nipples specifically, so take special note of any major changes to your nipples.