Acetaldehyde
Acetaldehyde is produced by the liver as it breaks down ethanol. The liver then normally eliminates 99% of the acetaldehyde. An average liver can process 7 grams of ethanol per hour. For example, it takes 12 hours to eliminate the ethanol in a bottle of wine, giving 12 hours or more of acetaldehyde exposure. A study of 818 heavy drinkers found that those who are exposed to more acetaldehyde than normal through a defect in the gene for alcohol dehydrogenase are at greater risk of developing cancers of the upper gastrointestinal tract and liver.
Read more about this topic: Alcohol And Cancer, Possible Mechanisms of Alcohol As A Carcinogen