Breast development is a complex biological process in primates that takes place throughout a female's life. It occurs across several phases, including prenatal development, puberty, and pregnancy. At menopause, breast development ceases and the breasts atrophy. Breast development results in prominent and developed structures on the chest known as breasts in primates, which serve as both a sexual characteristic and as mammary glands. The process is mediated by an assortment of hormones and growth factors, the most important of which include estrogen, progesterone, prolactin, growth hormone, and insulin-like growth factor 1.