Nipple hardness, pain specifically five major reasons: 1, premenstrual syndrome, endocrine reasons in the body hormone imbalance level fluctuation is too large, with cyclical with menstruation appears and disappears and disappears, often accompanied by the production of breast nodules. 2, high libido performance, in the high libido will appear nipple erection, red, swollen, swelling and pain, fever performance. 3, breast disease, such as cystic changes in the breast, breast fibroids and even breast cancer can lead to nipple hardness and pain. Breast cancer can all lead to hard and painful nipples. Lumps will appear in the breast and also painful manifestations, and breast cancer patients will even have orange peel-like changes in the breast skin.4. Breast trauma, excessive exercise can lead to nipple rupture and bleeding. If the breast is hit, there will be ecchymosis of the skin, and the nipple will be swollen and painful.5. Breast allergy, poor quality of underwear and contact with allergens may lead to breast allergy.