Hard lumps inside the nipple may be related to inflammation, trauma, swelling and other factors. 1. Mastitis: During breastfeeding, a large amount of milk accumulates in the body, which can easily cause inflammation of the mammary gland. Localized inflammation and irritation may lead to the formation of hard lumps inside the nipple. 2. Mammary gland trauma: After the nipple has suffered from impact injury or surgical injury, hematoma or scar will be formed locally, which will also lead to hard lumps inside the nipple. 3. Breast Hyperplasia: Abnormal hormone levels in the body, especially elevated levels of estrogen, may lead to hyperplasia of the breast tissue, which may also lead to hard lumps inside the nipple. There may be other clinical factors that can also lead to hard lumps inside the nipple. It is recommended to go to the breast surgery department of the hospital as soon as possible, and cooperate with the doctor to complete the relevant examinations to clarify the cause of the disease.