Suddenly there is no milk in one breast, which may be due to breast milk stagnation, acute mastitis and low milk secretion. 1. Milk stagnation: The baby’s prolonged sucking on one breast leads to excessive milk secretion from the other breast, which blocks the milk ducts and leads to the obstruction of milk discharge, so there will be no milk on one breast suddenly. 2. Acute mastitis: When a breastfeeding woman produces too much milk and her nipple is broken due to improper sucking, the airborne bacteria such as Staphylococcus aureus will be infected through the broken part, resulting in acute mastitis of the breast, and the ducts of the mammary glands will be blocked by increased secretion, so the breast will be empty all of a sudden. 3. Less milk secretion: Due to abnormal congenital development and other factors, one side of the breast is bigger and the other side is smaller, the milk secretion of the smaller side of the breast is less accordingly, so this symptom will appear. In addition, breast tumors, breast cysts and other diseases may also appear after the compression of the milk ducts, one breast suddenly no milk may be related to a variety of factors, it is recommended to consult a doctor for a clear diagnosis.