Estrogen is the primary sex hormone in women and it functions during the reproductive menstrual cycle. Women have three major types of estrogen: estrone, estradiol, and estriol, which bind to and activate receptors within the body. Researchers discovered the three types of estrogen over a period of seven years, contributing to more detailed descriptions of the menstrual cycle. Each type of estrogen molecule contains a slightly different arrangement or number of atoms that in turn causes some of the estrogens to be more active than others. The different types of estrogen peak and wane throughout women's reproductive cycles, from normal menstruation to pregnancy to the cessation of menstruation (menopause). As scientists better explained the effects of estrogens, they used that information to develop oral contraceptives to control pregnancy, to map the menstrual cycle, and to create hormone therapies to regulate abnormal levels of estrogen.

The figure depicts three different molecular structures of estrogen found in mammals’ that differ by the arrangement of bonds and side groups. The molecular structures of the three estrogen molecules differ by the arrangement of chemical bonds and side groups attached to the core steroid structure, cholesterol, which contains three cyclohexane rings and one cyclopentane ring.

Christine Jorgensen was a transgender woman and activist in the United States who lived during the twentieth century. She was one of the first US citizens to publicly disclose her gender transition from male to female through gender-affirming surgery and hormone replacement therapy. By 1949, when Jorgensen began her transition, few individuals had undergone gender transition. Various popular media outlets reported on Jorgensen’s gender transition and surgery, which allowed Jorgensen to educate the American public on topics such as gender identity and sexual orientation. Jorgensen authored an autobiography in 1967, which detailed the journey of her life from early childhood to the end of her forties. Although many transgender people continue to fight for acceptance and equality in the US as of 2024, Jorgensen’s advocacy and activism increased transgender awareness for the general public at a time when existing and living openly as a transgender person received little recognition and support.