Stand in front of a full-length mirror, look carefully at both breasts and examine your nipples. It's not necessarily abnormal if one nipple looks different from the other, but be alert for changes in the nipple that are possible signs of a problem. A nipple that becomes inverted, or turned inward, when it is not usually that way, is your signal to call your doctor. She will examine your breasts and order a mammogram or other tests to identify the reason for the inversion. The same goes for a nipple that looks crusted: let your doctor know right away.