There are many reasons why the two sides of the chest are not the same big: 1, congenital development is different. This is genetically determined, just like everyone’s feet are not the same size, belongs to the physiological phenomenon. 2, bad habits in life. For example, lying on the side leads to unilateral breast pressure, blood circulation is not smooth, it will appear than the other side of the breast small performance, change the sleeping position can. 3, unilateral breast disease. For example, unilateral breast hyperplasia, unilateral mammary fibromatosis or unilateral breast cancer formed by hard lumps, resulting in breast of different sizes, need to actively treat the original disease, if necessary, surgical plastic surgery. 4. dysplasia. In adolescent breast development breast disease, unilateral breast dysplasia, smaller than the other side, the difference is relatively large can be implanted breast augmentation. 5. breast size discrepancy due to milk stagnation, the need to promptly empty the stagnant milk.