Oestrogen (or estrogen) is a group of female hormones. It includes oestrone (E1), oestradiol (E2), and oestriol (E3). Oestradiol is the most important oestrogen.
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.