Heredity, (the way certain features such as eye color are passed down from generation to generation), is the most important factor in determining what the size and shape of your breasts will be. In general, young women have different breast sizes because of differences in families, hormones, and weight. There are no magic creams, special exercises, or clothing that will permanently change the size of your breasts. If your breasts have not started to develop, you may have a hormone imbalance. It’s a good idea to make an appointment with your health care provider to get checked.