Ketones are organic compounds in which a carbon atom is double bonded to an oxygen atom (carbonyl group) and to two carbon atoms, thereby distinguishing it from other oxygen containing compounds like carboxylic acids, aldehydes, esters, alcohols and ethers. The simplest ketone, acetone or propanone is a widely used solvent as is methyl ethyl ketone (MEK). Ketones also form in the body from the breakdown of fats and proteins in the liver and cause toxicity if present in excessive levels in the blood as can occur in diabetes and starvation.