Unilateral breast single hole extrusion of yellow pus is considered to be related to mastitis, ductal dilatation of the breast, breast cancer, lactinoma and so on. 1. Mastitis: the disease is related to bacterial infection, lactation stasis, breast trauma and so on. Typical symptoms of patients include breast swelling and pain, elevated skin temperature, breast overflow, etc. It can also be manifested as yellow pus extruded from a single hole in one breast. 2. Dilatation of mammary ducts: mainly related to the obstacle of mammary duct excretion, bacterial infection and other factors, common manifestations include nipple inversion, nipple discharge, lump under areola and so on. Some patients’ breast overflow can be manifested as yellow pus extruded from a single hole of one side of the breast. 3. Breast cancer: the cause of the disease is not clear, it may be related to genetic factors, exposure to radiation and so on. The disease can cause yellow pus from one hole of one side of the breast in some patients, and it is also easy to be accompanied by other symptoms such as breast lumps, breast skin abnormality, loss of appetite and weight loss. 4. Prolactinoma: the cause of the disease is not fully elucidated, the typical symptoms of the patients are breast overflow, menstrual disorders, weight gain, hirsutism, etc., which can also be manifested as yellow pus extruded from one hole of one side of the breast. In addition, breast hyperplasia and intraductal papilloma may also have similar clinical manifestations. It is recommended that patients with yellow pus coming out of a single hole of unilateral breast should consult a doctor for examination so as to clarify the cause of the disease and then follow the doctor’s instructions for treatment.