acetaldehyde
n. a toxic and volatile initial product of alcohol (ethanol) metabolism that is thought to be responsible for the alcohol flush reaction and certain other physical sequelae of alcohol consumption, including unpleasant effects such as nausea, vomiting, and headache. Acetaldehyde is produced when alcohol is broken down by a liver enzyme called alcohol dehydrogenase. It is then broken down by another liver enzyme (acetaldehyde dehydrogenase) into acetate and, ultimately, into carbon dioxide and water. Acetaldehyde is also a major component of tobacco smoke. It may influence the development, progression, and persistence of alcohol use and of tobacco use. See also disulfiram.