One breast is big and the other is small. The reason for the difference in breast size needs to be clarified, which may be due to congenital development, improper breastfeeding, or cystic hyperplasia of the mammary glands. According to different reasons to take different ways of treatment. 1. Congenital development: If one side of the patient’s breast is congenitally underdeveloped, it will lead to the phenomenon that one breast is big and the other is small. This situation generally does not need treatment, if the impact of aesthetics, the patient can go to the regular hospital to take breast augmentation surgery, the specific surgery needs to be based on the doctor’s diagnosis to choose. 2. Improper breastfeeding: if the patient is in the breastfeeding period, often use the same side of the breastfeeding, will lead to the phenomenon of milk on the other side of the breast, will also lead to a small breast. It is recommended that patients correct their breastfeeding habits in time and use both breasts for breastfeeding. 3. Breast cystic hyperplasia: If a patient has breast cystic hyperplasia on one side of the breast, the phenomenon of one breast being big and the other being small will also occur. Patients can follow the doctor’s instructions for drug treatment, but also can take surgical treatment, such as breast lumpectomy, mastectomy, simple mastectomy and other surgical methods. At the same time, the inconsistency between the two sides of the chest size may also be caused by breast tumors, which need to be clearly diagnosed in the hospital. When patients have inconsistent breast size, they need to consult regular hospitals in time to clarify the cause of inconsistency and then go through standardized treatment under the guidance of doctors.