Estradiol is a major female sex hormone and a type of estrogen steroid hormone. It is crucial in regulating the female reproductive system, including the menstrual and estrous cycles. Estradiol is responsible for the development of female secondary sexual characteristics such as breasts, widening of the hips, and a female pattern of fat distribution. It also plays a key role in the growth and maintenance of female reproductive tissues like the mammary glands, uterus, and vagina during puberty, adulthood, and pregnancy. Beyond reproduction, estradiol affects many other tissues, such as bone, fat, skin, liver, and the brain. It is produced mainly in the ovaries in females but also in smaller amounts in fat, adrenal glands, testicles (in males), and the brain. Estradiol levels rise during puberty and hormone cycles and decline significantly after menopause when ovulation stops. In addition to its natural roles, estradiol is used medically in menopausal hormone therapy and feminizing hormone therapy for transgender individuals. It can be delivered as oral tablets, skin patches or gels, vaginal creams, injections, or implants. Estradiol is the most potent and abundant estrogen during women's reproductive years and is derived in the body from cholesterol through enzymatic conversion pathways. In men, estradiol is present at much lower levels but still has important roles in physiological processes. Overall, estradiol is essential for reproductive health, secondary sexual characteristics, and has widespread effects on multiple organ systems.
