Cholesterol, from the Greek chole- (bile) and stereos (solid) followed by the chemical suffix -ol for an alcohol, is an organic chemical substance classified as a waxy steroid of fat. It is an essential structural component of mammalian cell membranes and is required to establish proper membrane permeability and fluidity. In addition, cholesterol is an important component for the manufacture of bile acids, steroid hormones, and vitamin D. Cholesterol is the principal sterol synthesized by animals, predominantly in the liver; however, small quantities can be synthesized in other eukaryotes such as plants and fungi. It is almost completely absent among prokaryotes, i.e. bacteria. Although cholesterol is important and necessary for the aforementioned biological processes, high levels of cholesterol in the blood have been linked to damage to arteries and cardiovascular disease.