Estrogen is primarily produced by the ovaries in females during their reproductive years, specifically by the granulosa cells of the ovarian follicles and the corpus luteum

. During pregnancy, the placenta also produces estrogen, notably the form called estetrol (E4)

. In addition to the ovaries, smaller amounts of estrogen are produced by other tissues such as the adrenal glands, adipose (fat) tissue, skin, bone, brain, and breasts

. The adrenal glands and adipose tissue are significant sources of estrone, especially after menopause when ovarian estrogen production declines

. The brain, particularly the hypothalamus, can also synthesize and release estrogen, which plays a role in regulating reproductive function and other physiological processes

. Estrogen biosynthesis involves conversion of androgens (like testosterone and androstenedione) to estrogens by the enzyme aromatase, which is expressed in the ovaries and extragonadal tissues such as adipose tissue and skin

. In summary, estrogen is produced mainly by:

• Ovaries (primary source in reproductive-age women)
• Placenta (during pregnancy)
• Adrenal glands
• Adipose tissue
• Skin, bone, brain, and breasts (minor sources)
• In males, estrogen is produced in small amounts by the testes and other tissues