Estrogen.

Estrogen is a class of hormones that plays an important role in female reproductive and sexual development. The estrogen class includes three specific hormones with related functions: estradiol, estriol, and estrone. Women produce these substances in varying amounts throughout their lives, with average levels of some estrogens rising during reproductive age and others being more prevalent after menopause. Puberty and pregnancy also affect the average production levels of particular estrogen hormones. Although estrogen is considered a class of female sex hormones, males produce small amounts of estrogen, and studies have shown that it plays a relatively limited but significant set of functions in their overall health. The main purpose of estrogen hormones is to regulate the growth, maintenance, and repair of the elements of the female reproductive system. It also helps develop female secondary sex characteristics and supports other sexual and reproductive functions. The estrogen hormone estradiol plays a key role in bone health. Scientists have identified several estrogen receptors, including estrogen receptor alpha (ERα), estrogen receptor beta (ERβ), and G protein–coupled estrogen receptor (GPER), in different tissues. These receptors help explain why estrogen affects the reproductive system, bones, the brain, and other organs in different ways.