The main component of alcohol is ethanol, which is first converted into acetaldehyde by ethanol dehydrogenase in the liver, then acetaldehyde is converted into acetic acid by acetaldehyde dehydrogenase, and finally carbon dioxide and water are produced. The redness of the face after drinking is related to the amount of acetaldehyde dehydrogenase in the human body. If there is less acetaldehyde dehydrogenase to break down acetaldehyde, more acetaldehyde will accumulate in the body, and acetaldehyde will stimulate the expansion of blood vessels, resulting in redness, and some will also have symptoms of intoxication such as rapid heartbeat and nausea, and these people have a small amount of alcohol.