 For example, some people (predominantly East Asians) have a mutation in their alcohol dehydrogenase gene that makes this enzyme unusually fast at converting ethanol to acetaldehyde.In addition, about half of all East Asians convert acetaldehyde to acetic acid more slowly (via acetaldehyde dehydrogenase), causing a higher buildup of acetaldehyde than normally seen in other groups.The high concentration of acetaldehyde causes the alcohol flush reaction, colloquially known as the "Asian Flush".