Causes of small breasts
The size of breasts is genetically determined. Once developed, the breasts may fluctuate in size in response to changes in weight, pregnancy and breast feeding.
The aging process causes the shape of the breast to change so that they gradually droop (called ptosis). This effect is greater following pregnancy, breast feeding and in particular after a large weight loss. Most women have breasts of slightly different sizes, but occasionally a very marked difference may develop.