Why Do Breasts Grow?
When girls hit puberty, estrogen is released into the body and the breasts begin to grow. This tends to coincide with the beginning of menstruation. As the breasts grow, the milk ducts in them increase in size, causing the breasts to expand at the nipple. Then the breast tissue itself expands. According to TeenGrowth.com, breasts grow for about five to six years and generally stop growing by age 17 or 18. This is the natural end to breast growth. However, some things can affect breast size outside of puberty.
In some cases, maintaining a poor diet can cause breast growth to be delayed. If you are deficient in vitamins, the proper hormones will not be released and the breasts will stop growing. This is easily remedied, however, by adopting a healthier diet.
Your breasts may stop growing simply due to genetics. Heredity determines how large your breasts grow. However, this doesn't mean you'll be a mirror image of your mother. When your hormones shut off the signal to keep your breasts growing, they stop growing. Your breast size may resemble any female in your family or none at all. Look to your grandmother or your aunts for an idea. Their size is likely to be close to yours.
Breasts can also stop growing due to hormone fluctuations throughout life. Even though your breasts might have stopped growing at age 18, they can start again during pregnancy. After breastfeeding, the breasts stop increasing in size and shrink. Likewise, taking birth control pills can increase your bust size temporarily until you go off the pill, at which time your breasts decrease and once again put an end to breast growth.