Breast Size. This occurs in response to hormonal changes in the body.
Hormonal Maturation. Actually a complicated answer. Starts at puberty->E2 causes a system of breast ducts to develop, then secretory glands that will store the milk develop by your first period & then group into sets of lobules. Each cycle progest causes these to enlarge (monthly breast pain), if no preg->back to nl. If preg E2/progest ?->matures ducts/glands/lobules. FSH,LH,Prolactin,oxytocin,HPL->milk prod->? size.