Estrogen

Estrogens, also called oestrogens, are the primary female sex hormone. While estrogens are present in both men and women, they are found in women in significantly higher quantities. They promote the development of female secondary sexual characteristics, such as breasts, and are also involved in the thickening of the endometrium and other aspects of regulating the menstrual cycle, which is why many oral contraceptives contain estrogens.

The three naturally occurring estrogens are estradiol, estriol and estrone. In the body these are all produced from androgens through enzyme action. Estradiol is produced from testosterone and estrone from androstenedione. Estrone is weaker than estradiol, and in post-menopausal women more estrone is present than estradiol.