Estrone (E1, and also oestrone) is an estrogenic hormone secreted by the ovary as well as adipose tissue with the chemical name of 3-hydroxyestra-1,3,5(10)-triene-17-one and the chemical formula C₁₈H₂₂O₂. Estrone is an odorless, solid crystalline powder, white in color with a melting point of 254.5 °C and a specific gravity of 1.23. Estrone is one of several natural estrogens, which also include estriol and estradiol. Estrone is the least abundant of the three hormones; estradiol is present almost always in the reproductive female body, and estriol is abundant primarily during pregnancy.