There are genetic variations in alcohol metabolizing enzymes that result in slower removal or faster production of acetaldehyde. The build up of acetaldehyde triggers an aversive reaction that results in less alcohol use and reduces the development of alcoholism.Alcohol is metabolized to acetaldehyde by alcohol dehydrogenase (ADH) and acetaldehyde is metabolized to acetic acid by acetaldehyde dehydrogenase (ALDH).Following alcohol, less activity of ALDH results in increased levels of acetaldehyde, which produces intense unpleasant symptoms of flushing, perspiration, dizziness, headache, tachycardia and nausea and vomiting.Individuals with genetic variations in the ALDH gene that impair ALDH function experience these distressing symptoms after drinking alcohol and subsequently avoid alcohol consumption. Those homozygous for the lowest activity allele are almost fully protected from developing alcoholism.Individuals with variations in the ADH gene that increase the rate of metabolism of alcohol to acetaldehyde are also protected from developing alcoholism, but to a lesser extent.There is evidence that some of the variations in the ALDH and ADH genes are independent factors in reducing the development of alcoholism.