Testosterone can stimulate hair growth, estrogen can activate breast tissue enlargement, and prolactin can control milk production.

“So for instance, a good example of this outside of the context we've been talking about is the hormone testosterone can travel to the hair follicle and can stimulate changes in the genes of the cells of the hair follicle that can make hair grow. A different hormone, estrogen, can travel to the cells of the breast tissue and activate genes that control enlargement of the cells of the breast tissue. Prolactin, a different hormone, can travel to the mammary ducts and control the production and the secretion of milk.”