Mammoplasia is a big word that talks about how a girl's breasts grow into woman's breasts when she grows up. Just like getting taller or growing hair, some parts of a girl's body change as she gets older and one of those changes is her breasts. When she hits puberty, her body starts to make hormones that help her breasts get bigger and grow into the shape of a woman's breasts. This is called mammoplasia. Basically, it is the process of the body developing and growing the breasts to get ready for adulthood.