Smaller breasts are considered to be caused by the following conditions: First, it is considered to be caused by weight loss, which is due to the fact that breasts are composed of fatty tissue as well as breast tissue, and after weight loss, there will be a reduction of fat in the breasts. If you lose weight during this time, the lack of nutrition will cause a decrease in breast tissue, making the entire breast structure less, resulting in smaller breasts. Second, it may be due to incorrect exercise that leads to smaller breasts. Third, consider the smaller underwear, which hinders the normal development and growth of the breasts, making the breasts appear smaller. It may be due to unbalanced diet, or it may be caused by breast disease, such as breast enlargement or breast cancer. It is best to go to the hospital for further examination and, if necessary, take appropriate treatment.