Estrogens are a group of hormones that play an important role in the normal sexual and reproductive development in women. In addition to regulating the menstrual cycle, estrogen affects the reproductive tract, the urinary tract, the heart and blood vessels, bones, breasts, skin, hair, mucous membranes, pelvic muscles, and the brain. Secondary sexual characteristics, such as pubic and armpit hair, also start to grow when estrogen levels rise. Many organ systems, including the musculoskeletal and cardiovascular systems, and the brain are affected by estrogen.

There are three main types of estrogen:

Estradiol is the primary form of estrogen that’s made during a woman’s reproductive years (by the ovaries).

Estriol is the primary form of estrogen that is made during pregnancy (by the placenta).

Estrone is the primary form of estrogen that a woman’s body produces post-menopause (primarily in fat tissue as well as the adrenal glands).

Estrogens have traditionally been considered female hormones, but men have them also. The two main types of estrogen in men are estrone and estradiol, and it is estradiol that is especially crucial to male sexuality.