Cholesterol is a steroid alcohol that is essentially insoluble in aqueous solutions. In mammals it is normally solubilized by its association with other lipids, such as phospholipids or bile acids; thus, most cholesterol is found in cell membranes, plasma lipoproteins, and bile. Cholesterol can be esterified with a fatty acid to form cholesteryl esters. The latter form discrete lipid droplets in cells, especially in cells of steroidogenic tissues, and in the lipid core of low-density lipoproteins in the blood.