The causes of breast asymmetry include: 1, congenital factors, in the human embryonic development, if there is an abnormal development of one side of the breast, there will be a problem of a large breast and a small breast. In addition, the breast development during puberty, due to the body’s estrogen, progesterone, resulting in the development of sensitive and strong side of the breast development too fast, while the other side of the breast development is too slow, will also lead to a large breast and a small breast problem. 2, acquired factors, which mainly occurs in women who have given birth to breastfeeding, feeding children with one breast or breastfeeding incorrect posture, will lead to breast atrophy 3, the usual sports posture, the amount of exercise and sleep posture is not correct, it will lead to uneven development of the pectoral muscle on both sides of the breast. The appearance of these problems can also be achieved through acquired breast augmentation surgery to achieve symmetrical plumpness of both breasts, and patients need not worry too much.