The causes of nipple pain are related to premenstrual syndrome, mastitis and breast cancer. 1. Premenstrual syndrome: Before a woman’s menstrual cycle, the level of estrogen in her body will rise, and estrogen will stimulate the breast tissue, resulting in hyperplastic swelling and pain in the breast. After menstruation, the hormone level will return to normal and the pain will disappear. 2. Mastitis: Mastitis is an inflammation of the breast tissue and is divided into lactating mastitis and non-lactating mastitis. Breastfeeding mastitis will show redness, swelling, heat, and pain in the breast, while non-breastfeeding mastitis may show symptoms such as lumps and pain. 3. Breast Cancer: Breast cancer is the most common malignant tumor in women and is caused by the uncontrolled proliferation of epithelial cells in the breast, which can lead to malignant changes. Breast cancer can cause localized symptoms such as breast lumps, breast skin abnormalities, and breast pain. In addition, nipple eczema, nipple trauma, breast hyperplasia and other diseases may also cause nipple pain, causing nipple pain of different causes, the specific treatment will also be different, do not recommend that the patient self-treatment, it is recommended that patients go to the hospital in a timely manner to seek medical treatment.