The common clinical causes of hard nipples are breast hyperplasia, nipple inflammation and breast cancer. 1. Mammary hyperplasia: This is the most common benign breast disease, mostly seen in women aged 30 to 50, usually associated with endocrine dysfunction, clinical manifestations of breast pain, lumps or nodules, and part of the population is also accompanied by nipple pain, overflow and other symptoms. 2. Nipple inflammation: this disease is usually caused by secondary infection of cracked nipples, mostly seen in breastfeeding primigravid women, with clinical manifestations of red, swollen, painful and cracked nipples. 3. Breast Cancer: This refers to the phenomenon of uncontrolled proliferation of mammary epithelial cells under the action of various carcinogenic factors. Early clinical manifestations of the diseased population include breast lumps, enlarged lymph nodes in the armpits, and nipple overflow, etc. Hard lumps can be touched on physical examination, and the diseased population will also be accompanied by symptoms of tenderness and pressure pain. In addition, trauma to the breast, mastitis, breast cysts and other similar symptoms may also occur, if the above conditions exist, it is necessary to consult a doctor in a timely manner to clarify the diagnosis and take targeted treatment.