The chest pain nipple out of water is considered to be caused by mammary gland hyperplasia, mastitis, mammary gland tumor and so on. 1. Mammal hyperplasia: the cause of the disease is mostly related to endocrine dysfunction, which may be caused by the imbalance of the ratio of estrogen and progesterone, or it may be caused by the elevation of prolactin, etc., which often leads to breast pain, nodules, lumps, and nipple discharge in some patients. 2. Mastitis: If mastitis occurs during breastfeeding, it is mostly caused by bacterial invasion or milk stagnation. The cause of non-lactating mastitis is not clear, but it may be related to bacterial infection and blocked milk ducts, which is often manifested as redness, swelling, heat and pain in the breasts, and sometimes accompanied by nipple discharge. 3. Breast tumors: including benign and malignant tumors, the etiology is still unclear, benign tumors patients mostly have no obvious self-conscious symptoms, but in the case of malignant tumors and breast cancer, the late stage of the chest pain may occur, and accompanied by nipple water. The pain in the chest and the water in the nipple may be caused by other reasons, so it is recommended that you go to the hospital in time to clarify the cause and then take targeted treatment.