Cholesterol is a lipid. It is a waxy, fat-like substance that is produced by the liver and can be obtained through eating certain foods. While it is an important part of a person's diet and overall health, it also plays an important role in the cell membrane. The cell membrane is a selectively permeable membrane, and its permeability is regulated by cholesterol in the membrane itself as well as proteins and lipoproteins. A cell with too little cholesterol in the membrane would cause the cell membrane to be too permeable, and the cell would leak far too many fluids and molecules in and out of the cell. Too much cholesterol would cause the cell membrane to be less fluid and more rigid. This would cause the membrane to become less permeable, and the cell might not be able to regulate fluid and molecule balance as efficiently.