Drinking alcoholic beverages can be a pleasurable activity for some, while the same activity can be very unpleasant for others, due to the body’s adverse reaction to alcohol. This hypersensitivity reaction to alcohol manifests itself even when drinking minimal amounts of alcohol and usually results in a reddening of the face, accompanied by a feeling of warmth and stinging. People suffering from alcohol hypersensitivity often experience other symptoms in response to alcohol intake, such as rapid heartbeat, nausea, dizziness and severe hangovers. Alcohol metabolism is carried out by two enzyme systems in the liver: alcohol dehydrogenase and aldehyde dehydrogenase enzymes, encoded by the ADH and ALDH genes, respectively. For the ALDH2 gene, a variant associated with alcohol hypersensitivity has been discovered. This is the rs671 variant. If your genotype is AA or AG, you have a genetic predisposition to develop episodes of alcohol hypersensitivity in response to alcohol intake. The A allele codes for a defective form of the enzyme alcohol dehydrogenase. This causes alcohol to be inefficiently metabolised and accumulate in the blood, causing the dreaded hangover, which can manifest with headache, dizziness, nausea, fatigue, as well as sensitivity to light and sound. If your genotype is GG, you have a lower genetic predisposition to develop these hypersensitivity episodes in response to alcohol consumption.