primary female sex hormone in mammals, as well as a medication, is responsible for the development and regulation of the female reproductive system and secondary sex characteristics

Oestrogen (or estrogen) is a group of female hormones.[1] It includes oestrone (E1), oestradiol (E2), and oestriol (E3). Oestradiol is the most important oestrogen. Oestrogen is mainly secreted by the ovary, a small amount by the liver, adrenal cortex, and breast. In pregnancy, the placenta can also have a lot of secretion. Male testes also secrete a small amount. Ovary mainly secretes β-estradiol, other estrogens are less important.[2]

Oestrogen helps women grow during puberty and is part of the menstrual cycle. During menopause, oestrogen levels go down. The male hormone that is similar is androgen.


  1. The word comes from the Greek οἶστρος, meaning gadfly. Its use here is not literal.
  2. Whitehead S.A. & Nussey S. 2001. Endocrinology: an integrated approach. Oxford: BIOS. ISBN 1-85996-252-1