The causes of breast asymmetry are divided into congenital and acquired, including Poland syndrome, glandular bud necrosis, etc. The details are as follows: I. Congenital for Poland syndrome, that is, breast pectoral muscle deformity, dysplasia, or even only the nipple without any glandular tissue, and even the chest wall will collapse. The lighter patients have small breasts, asymmetry on both sides and normal development of the opposite side of the breast; 2. Acquired can be seen in the following cases: 1, high estrogen in the mother’s body at birth, resulting in small hard knots in the baby’s breasts, and at this time, extrusion of the breast nucleus will cause necrosis of the mammary germ, and after puberty, the original mammary germ will be damaged, and the breasts on this side may be poorly developed, small, and asymmetric; 2. Inflammation, tumors can cause Inflammation and tumor will cause edema of the skin on one side of the breast, and the breast will be enlarged, and there will be a local protrusion; 3. Long-term use of one breast for breastfeeding, and the breast on the side of breastfeeding may be large and sagging, which will also cause asymmetry. Therefore, breast asymmetry may be a disease or a habitual cause, so it is necessary to go to a specialist to distinguish the cause and treat it differently.