The main reason for the formation of bilateral asymmetry of the chest is caused by bilateral developmental variability, not only the woman’s chest will appear this variability, anyone bilateral organs are not completely symmetrical, just the size of the variability makes a difference. The reasons for the formation of bilateral variability are the following: 1, genetic decision, genetic inheritance of bilateral is not completely symmetrical, even if the decision of bilateral organs of the gene symmetry, in the expression of the expression of asymmetry may also occur; 2, acquired development of bilateral breasts are subjected to different levels of hormonal stimulation, the development of women’s breasts and the level of estrogen has a lot to do with. If the level of estrogen is not enough during breast development, or the stimulation of bilateral breasts is not balanced at all, there will be obvious asymmetry on both sides; 3. Missing or unbalanced absorption of materials needed for breast development, such as proteins affecting the development of breasts are not sufficiently replenished during the development of breasts, and the whole of the body is at the level of deficiency, resulting in poor breast development and uneven size on both sides. Different levels of absorption on both sides can also show obvious differences.