Why Some People Turn Red When They Drink: The ALDH2 Variant

A few sips of wine and your face goes red, your heart starts pounding, and you feel warm and slightly sick. If that's you, the cause is very likely a single letter change in a gene called ALDH2, specifically the variant known as rs671. It's carried by a large share of people with East Asian ancestry, and it changes how the body handles a toxic byproduct of alcohol called acetaldehyde.

What actually happens in the body

When you drink, your liver converts alcohol (ethanol) into acetaldehyde, then normally breaks that acetaldehyde down further into harmless acetate. The enzyme responsible for that second step is aldehyde dehydrogenase 2, or ALDH2. People who carry the rs671 variant produce a version of ALDH2 that barely works. Acetaldehyde builds up in the blood instead of clearing quickly, and acetaldehyde itself is what triggers flushing, a racing pulse, nausea, and headache. Researchers at the University of Bristol and Oxford, writing in a 2023 BMC Genomics study, describe it directly: "Genetic variants in ALDH2 and ADH1B alter alcohol metabolism leading to prolonged, elevated levels of acetaldehyde," and it's that excess acetaldehyde driving the reaction (Cho et al., 2023).

This is different from a general alcohol intolerance or an allergy. It's a specific enzyme deficiency, and it's genetic, not something you develop or grow out of.

Why this variant shows up mostly in East Asian populations

The rs671 variant is common in people with Chinese, Japanese, and Korean ancestry, and much rarer in other populations. A 2022 review from Stanford's Department of Chemical and Systems Biology, published in Disease Models & Mechanisms, notes that carrying the ALDH2*2 variant "can lead to alcohol avoidance due to the unpleasant alcohol flushing response" (Chen et al., 2022). That avoidance effect is actually part of why researchers find the variant scientifically interesting: it's a rare case where a person's genetics directly shape their drinking behavior, rather than only their risk once they've had a drink.

Heart rate and hypertension risk

The physical effects go beyond turning red. A STROBE observational study of Korean adults found the rs671 polymorphism is "primarily associated with cancer and alcohol consumption in Asians... and increased heart rate when alcohol is consumed" (Kim et al., 2021). That same study looked at how rs671 interacts with lifestyle factors and found it affects hypertension risk. The variant's effects extend past an uncomfortable evening into measurable cardiovascular strain, particularly in people who continue to drink despite the reaction.

There's also a metabolic angle few people expect. A 2023 study of middle-aged and elderly Japanese adults who routinely drink found that carriers of the rs671 variant allele had higher energy intake, with researchers reasoning that detoxifying acetaldehyde may raise the body's energy demands (Hayashida et al., 2023).

The cancer risk connection

This is the part of the ALDH2 story that gets the most public health attention, and for good reason. Because acetaldehyde is a recognized carcinogen, people who carry rs671 and keep drinking anyway are exposing their tissues to higher, more prolonged acetaldehyde levels than non-carriers, particularly in the esophagus. A 2026 letter in Public Health Genomics from Northwestern University's Center for Genetic Medicine argues the flushing response should be treated less as a curiosity and more as a clinical signal, describing it as "a noninvasive biomarker for ALDH2 deficiency, allowing healthcare providers to screen high-risk patients" (Young and Seung, 2026). In other words, the flush itself can be a useful, visible clue that someone is carrying elevated cancer risk tied to continued alcohol exposure.

Flushing and alcohol dependence risk

There's a counterintuitive finding buried in the Japanese research literature. You'd expect that people who flush and feel sick would drink less, and often they do. But a study of Japanese men and women examining flushing status alongside ALDH2 and ADH1B genotypes found that combining flushing history with genotype data "may have a better performance for predicting the alcohol-dependence risk" than either factor alone (Yokoyama et al., 2021). Some carriers drink through the discomfort over time, and that group appears identifiable partly through this combined flushing-plus-genotype profile. It's a reminder that "genetically protected against heavy drinking" isn't true for everyone who carries the variant.

What to actually do with this information

If you flush when you drink, the practical takeaway from this research is straightforward: acetaldehyde buildup is uncomfortable, but it's also a signal worth taking seriously, especially around long-term drinking habits. None of this means a flushing reaction diagnoses a disease or predicts an individual's cancer risk with certainty. It means the population-level evidence linking rs671, acetaldehyde exposure, and cardiovascular and cancer risk is well established enough that clinicians increasingly treat the flush as more than a party inconvenience.

Genetic testing can confirm whether the rs671 variant is present. Biome's DNA panel reports on this exact marker under "Alcohol flush response," using ALDH2 rs671, an evidence tier the panel classifies as high confidence when the variant is observed. Whether you get that information from a DNA test or simply from noticing your own reaction pattern, the underlying biology is the same.

On privacy: reputable DNA testing companies typically publish specifics on how samples and genetic data are stored, whether they're shared with researchers, and what happens if law enforcement requests access. That varies by company, so check the specific service's own privacy policy rather than assuming.

FAQ

Is alcohol flush reaction genetic or an allergy? It's genetic, not an allergy. It comes from a variant in the ALDH2 gene, rs671, that slows the breakdown of acetaldehyde, the toxic byproduct alcohol turns into during metabolism (Cho et al., 2023).

Why do mostly East Asian people get this reaction? The rs671 variant is far more common in people with Chinese, Japanese, and Korean ancestry than in other population groups, which is why the flushing response is sometimes called the "Asian flush" (Chen et al., 2022).

Does alcohol flush reaction mean higher cancer risk? Carrying the ALDH2 variant and continuing to drink is linked to higher acetaldehyde exposure, and researchers have proposed using the flushing response as a screening signal for people at elevated risk (Young and Seung, 2026). It is not a diagnosis on its own.

Can you build a tolerance to alcohol flush reaction? The underlying enzyme deficiency doesn't change over time, but some people who carry the variant continue drinking despite the discomfort. Research on Japanese drinkers suggests flushing history combined with genotype helps predict alcohol dependence risk in that group (Yokoyama et al., 2021).

Can a DNA test tell me if I have the ALDH2 variant? Yes. DNA panels that report on rs671 can identify whether you carry the variant associated with alcohol flush response. Biome's DNA panel includes this marker under "Alcohol flush response."