Register for a free hard black nipple Sign hard black nipple for a free Medical News Today account to customize your medical and health news experiences. Any medical information published on this website is not intended as a substitute for informed medical advice and you should not take any action before consulting with a healthcare professional. These alterations occur because the menstrual process is driven by changes in hormone levels in the body. It may be noticed, during pregnancy, that the breasts become sore and swell. Nipples naturally change in color over time and due to many different biological events during a person's life.