A very serious milk blockage with large hard lumps is usually caused by acute mastitis, breast cancer, breast hyperplasia and other diseases. 1. Acute mastitis: Acute mastitis is usually a bacterial infection caused by the accumulation of milk, which usually manifests itself in symptoms such as hard lumps in the breasts and enlarged breasts. 2. Breast cancer: Breast cancer is a malignant tumor of the epithelial tissue of the breast, which may be formed by the malignant transformation of ductal or lobular epithelial cells. It is usually manifested by symptoms such as abnormal nipple and areola, accompanied by fatigue and poor appetite. 3. Mammary hyperplasia: Mammary hyperplasia is usually related to endocrine hormone levels and other factors, usually manifested as unilateral or bilateral breast pain and other symptoms, accompanied by nipple overflow and other manifestations. Blocked milk is very serious with large hard lumps may also be caused by breast fibroadenoma, breast trauma, etc. It is recommended that patients go to the hospital in time for diagnosis and treatment under the guidance of the doctor.