"Estrogens" are a family of related molecules that stimulate the development and maintenance of female characteristics and sexual reproduction.

The natural estrogens produced by women are steroid molecules, which means that they are derived from a particular type of molecular skeleton containing four rings of carbon atoms, giving the shape shown here. The most prevalent forms of human estrogen are estradiol and estrone. Both are produced and secreted by the ovaries, although estrone is also made in the adrenal glands and other organs.