What causes a difference in the sizes of the breasts in a person?
Most doctors assume that breast size differences are either genetic tendencies or random events in which paired organs like the breasts just grow differentially with respect to starting and stopping. The breasts are stimulated to grow under the influence of estrogen hormone in young girls. It begins with breast budding and about two years after that the first menstrual period occurs. The breast continues to grow for about 2-4 more years and it is during that time that there can be differences in size. Catchup growth does take place but if you are now 21 years old and breast development has gone on more than about 6 years, then it is unlikely to change now until pregnancy or menopause. Those are the other two events that can change size and shape of the breasts. A rule-of thumb that is commonly used is that most breast size differences are less than a bra cup size in volume and usually do not require surgical treatment. If you think your one breast is a full cup size or more different,
