Sudden swelling of milk with hard lumps after six months of weaning may be due to chronic mastitis, breast hyperplasia and breast cancer. 1. Chronic mastitis: Chronic mastitis, such as plasma cell mastitis, causes lumps in the breasts and nipple discharge six months after weaning, and the nipple discharge is characterized by purulent or milky fluid. 2. Mammary hyperplasia: Mammary hyperplasia will lead to breast nodules, causing breast lumps, breast pain and nipple discharge. 3. Breast Cancer: Sudden swelling and hard lumps in the breast half a year after weaning may also be due to breast cancer. Breast cancer is a malignant tumor lesion that usually grows faster. In addition, breast fibroadenoma, breast ductal papilloma, etc. will also appear after weaning breast hard lumps. There are many reasons for the sudden swelling and lumps after six months of weaning, and it is recommended that this condition requires prompt medical attention, and reasonable and standardized treatment under the guidance of a professional physician after a clear diagnosis.