Estrogen is a steroid hormone that is produced primarily by the ovaries in females and the testes in males, as well as by other tissues such as fat, bone, and the brain. It is involved in a variety of physiological processes beyond reproductive development, including maintaining cardiovascular health, supporting cognitive function, and modulating immune responses. Abnormal levels of estrogen have been linked to a wide range of conditions, including infertility, breast and ovarian cancer, osteoporosis, and cardiovascular disease.