One side of the breast is big and the other side is small, it may be a normal phenomenon, or it may be caused by breast disease, breastfeeding, etc. If necessary, it can be treated by medication and surgery. 1. Normal phenomenon: women’s two sides of the breast development will not be exactly the same, generally have a small phenomenon, if not obvious, there is no obvious discomfort symptoms, do not worry too much. 2. Breast diseases: when there are breast nodules, breast fibroids, breast hyperplasia, mastitis, breast cancer and other diseases, can cause the affected side of the breast is larger, and can touch the foreign body or accompanied by pain, need to be carried out breast ultrasound and pathological biopsy to identify the cause of the disease, the next step in the treatment. If it is acute mastitis, generally take penicillin anti-inflammatory treatment, if the formation of abscess, then need to carry out local abscess incision and drainage. 3. Breastfeeding: Breastfeeding women may have different sizes of breasts due to the strong secretion of milk, and the breasts may temporarily become smaller after the baby sucks up the milk from one side, in which case you don’t need to worry too much, and breastfeeding can be done normally. It is recommended that women should not blindly use medication on their own, but go to the breast surgery department for further examination, and if the disease is caused by the disease, they should follow the doctor’s instructions to use medication or surgical treatment.