Estrogen

Estrogens (alternate spellings: oestrogens or œstrogens) are a group of steroid compounds, named for their importance in the estrous cycle, and functioning as the primary female sex hormone.

Estrogens are used as part of some oral contraceptives, in estrogen replacement therapy of postmenopausal women, and in hormone therapy for transsexual women.

Like all steroid hormones, estrogens readily diffuse across the cell membrane; inside the cell, they interact with estrogen receptors.