ANDY'S ANSWER: Estrogen is is actually a group of chemically similar hormones estradiol, estrone and estradiol, which are the primary sex hormones in women. (Men also have estrogen, but in much smaller amounts.)
Estrogens trigger female characteristics during puberty such as breast growth, pelvis widening, and added fat in the hips and bum areas. Estrogen is also the hormone that is responsible for women having smoother skin and less body hair than men. It is an essential part of reproduction and regulates a woman's menstrual cycle and helps prepare the uterus for pregnancy. A woman's body produces the greatest amount of estrogens during the reproductive years.