Inverted nipple with bitter water may be caused by sebaceous cyst, mastitis and breast cancer. 1. Sebaceous cysts: sebaceous glands will secrete some fat particles, blocking the pores to form cysts, which are accompanied by odor and bitter water in addition to secretions. 2. Mastitis: Breastfeeding women have difficulty in discharging milk due to inverted nipples, and the milk stagnates in the breasts, causing mastitis, which is characterized by the symptom of bitter water, accompanied by nipple pain and nipple discharge. 3. Breast cancer: Breast cancer often occurs near the nipple or areola. When the cancer enters into the milk ducts and shortens the milk ducts, the symptoms of nipple inversion will appear, accompanied by the phenomenon of bitter water. When the patient has the symptoms of nipple inversion with bitter water, it is recommended to go to the hospital immediately for examination and diagnosis, and carry out appropriate treatment under the guidance of doctors after the cause of the disease is clarified.