[4][6][7] The reaction is informally termed Asian flush due to its frequent occurrence in East Asians, with approximately 30 to 50% of Chinese, Japanese, and Koreans showing characteristic physiological responses to drinking alcohol that includes facial flushing, nausea, headaches and a fast heart rate.

[9] People affected by this condition show greater reduction in psychomotor functions on alcohol consumption than those without.

According to the analysis by HapMap project, 20% to 30% of people of Chinese, Japanese, and Korean ancestry have at least one ALDH2*2 allele, while it is rare among Europeans and sub-Saharan Africans.

[5] The reasons for this positive selection are not known, but it has been hypothesized that elevated concentrations of acetaldehyde may have conferred protection against certain parasitic infections, such as Entamoeba histolytica.

[14] Additionally, in around 80% of East Asians, the rapid accumulation of acetaldehyde is worsened by another gene variant; in this case the allele ADH1B*2, which results in the alcohol dehydrogenase enzyme converting alcohol to toxic acetaldehyde more quickly than other gene variants common outside East Asia.

Homozygotes for the trait find consumption of large amounts of alcohol to be so unpleasant that they are generally protected from esophageal cancer, but heterozygotes are able to continue drinking.