Hard things inside the nipple may be: 1. Normal development during puberty. The fluctuating level of hormones during puberty is relatively large, and hard things in the nipples are a developmental manifestation, so there is no need to worry. Boys may also appear, but with the development, the body of testosterone will prevail, nipple symptoms will disappear. 2, mastitis. If the nipple has had a rupture, bacteria will enter through the rupture to cause mastitis, and there will be hardness in the nipple. If the milk is stagnant, it provides a perfect environment for bacteria to grow and produce pus, which needs to be controlled in a timely manner and the pus eliminated.3. Breast cancer. Cancer patients may show no pain, tingling, swelling and pain in the breast, while the nipple is hard and swollen, and hard objects can be seen in the nipple. You need to go to the referral hospital in time, do the relevant examination, and then actively carry out surgical treatment or chemical drug treatment.