Breasts consist of skin, glandular tissue, connective tissue, ductal lobule units, ligaments, and fat. While breasts are always changing, they’re not considered completely mature until pregnancy or lactation occurs. “The ductal lobule units don’t get mature until they get the signal of lactation, or sometimes they just give up and fully mature about two years after we start our menstrual period,” says Amanda Wheeler, MD, breast surgeon at Stanford Health Care and clinical assistant professor of surgery at the Stanford University School of Medicine in California.
