Estrogen is not a single hormone but rather a family of hormones. Estradiol, estrone, estriol and estetrol regulate various organ systems in the body, affecting reproduction and the urinary tract, pelvic muscles, skin, hair, blood vessels and the heart, and the brain. They can also contribute to a healthy libido and sexual function. As with all hormones, we want estrogen in balance; in excess, it can cause bloating, mood swings, increased stress and headaches. Low estrogen activity can cause irritability, weak, brittle bones, difficulty concentrating and dry skin.