ALDH2 deficiency is a genetic condition in which your body can’t efficiently break down acetaldehyde, a toxic byproduct of alcohol metabolism. It affects roughly 8% of the world’s population, with the highest prevalence among East Asian populations, where up to half of some groups carry the gene variant responsible. The most recognizable sign is facial flushing after drinking alcohol, but the condition carries health consequences that go well beyond turning red.
How Your Body Normally Processes Alcohol
When you drink alcohol, your liver breaks it down in two steps. First, an enzyme converts the alcohol into acetaldehyde, a compound that is toxic to your cells, damages DNA, and triggers inflammation. In the second step, another enzyme called ALDH2 quickly converts that acetaldehyde into acetic acid, which is essentially harmless vinegar that your body can easily dispose of.
In people with ALDH2 deficiency, that second step stalls. Acetaldehyde builds up in the bloodstream instead of being cleared, and the more you drink, the more it accumulates. This buildup is directly responsible for both the immediate symptoms and the long-term health risks associated with the condition.
The Genetic Variant Behind It
ALDH2 deficiency is caused by a single-point mutation in the ALDH2 gene, producing what researchers call the ALDH2*2 variant. You inherit one copy of the gene from each parent, so there are two possible forms of the deficiency. People who carry one copy of the variant (heterozygous) have roughly 40 to 60% reduced enzyme activity. People who carry two copies (homozygous) have almost no functional ALDH2 activity at all and typically find even small amounts of alcohol extremely unpleasant.
The variant is concentrated in East Asian populations. Among Japanese people, 41 to 52% carry at least one copy. About one-third of Han Chinese and Korean populations carry it. Prevalence is lower in Thai populations (around 10%) and nearly absent in Filipino, Indian, and indigenous Taiwanese groups. The variant is rare in people of European or African descent.
What the Flush Reaction Feels Like
The hallmark symptom is the “alcohol flush reaction,” sometimes called “Asian glow.” Within minutes of drinking, acetaldehyde flooding your system causes blood vessels near the skin to dilate, producing visible redness across the face, neck, and sometimes the chest and shoulders. But flushing is only the most obvious symptom.
The reaction can also include nausea, a rapid heartbeat, low blood pressure, hives, headache, and worsening of asthma symptoms. Some people experience migraines. The severity depends on how much enzyme activity you retain. If you carry two copies of the variant, even a sip of beer can trigger intense discomfort. With one copy, you may tolerate small amounts but still flush noticeably and feel unwell compared to someone with full ALDH2 function.
Elevated Cancer Risk
The most serious long-term consequence of ALDH2 deficiency is an increased risk of esophageal cancer, particularly in people who drink despite the flush reaction. Acetaldehyde is classified as a Group 1 carcinogen, meaning there is strong evidence it causes cancer in humans. When your body can’t clear it efficiently, your esophagus and upper digestive tract are exposed to higher concentrations every time you drink.
A meta-analysis published in the World Journal of Gastroenterology found that people carrying one copy of the ALDH2*2 variant had roughly 2.5 times the risk of esophageal cancer compared to people with fully functional ALDH2. Among drinkers with two copies, the risk climbed to more than four times higher. This makes ALDH2 deficiency one of the strongest genetic risk factors for esophageal squamous cell carcinoma, and the risk is compounded by regular alcohol consumption. People who flush but continue to drink heavily face a dramatically higher cancer risk than either non-drinkers or drinkers with normal ALDH2 function.
Heart Disease and Other Health Effects
Beyond cancer, the accumulation of acetaldehyde and related toxic compounds called reactive aldehydes affects the cardiovascular system. Research published in the Journal of the American Heart Association found that carriers of the ALDH2*2 variant had a significantly higher risk of a specific type of heart attack caused by coronary artery spasm, in which blood vessels feeding the heart suddenly constrict. The frequency of the ALDH2*2 variant was notably higher in heart attack patients than in people without ischemic heart disease (about 30% vs. 24%).
Importantly, the link wasn’t explained by the usual heart disease risk factors. Patients with and without the variant had similar blood pressure, cholesterol, blood sugar, and smoking rates. This suggests that the buildup of reactive aldehydes from impaired ALDH2 activity is itself a direct contributor to coronary spasm and heart attack risk, independent of traditional cardiovascular risk factors. Studies have also reported associations between the variant and essential hypertension, and animal research shows that the toxic byproducts normally cleared by ALDH2 can worsen cardiac function over time.
How ALDH2 Deficiency Is Detected
The simplest screening method is the alcohol patch test. A small gauze pad soaked in ethanol is taped to the inner arm for about 15 minutes, then removed. If the skin underneath turns red, it suggests reduced ALDH2 activity. Studies have found this test has a sensitivity of about 82 to 86% and a specificity around 97%, meaning it catches most cases and rarely produces false positives. It’s a quick, inexpensive way to screen, though genetic testing through a blood or saliva sample provides a definitive answer by identifying whether you carry one or two copies of the ALDH2*2 variant.
Many people with the deficiency already suspect they have it based on their reaction to alcohol. If you consistently flush, feel nauseated, or get a rapid heartbeat after even moderate drinking, there’s a strong chance you carry the variant, especially if you’re of East Asian descent.
Living With ALDH2 Deficiency
There is currently no medication or treatment that restores normal ALDH2 enzyme function. The most effective way to avoid acetaldehyde-related harm is to reduce or eliminate alcohol consumption. This is especially important given the cancer and cardiovascular risks: the flush reaction is not just an inconvenience but a visible warning that a carcinogen is accumulating in your body.
Some people take antihistamines before drinking to suppress the visible flushing. This masks the redness but does nothing to reduce acetaldehyde levels. In fact, it may be counterproductive. Without the discomfort of flushing as a natural deterrent, people may drink more and expose themselves to greater acetaldehyde buildup without realizing it.
It’s also worth knowing that acetaldehyde exposure isn’t limited to alcohol. Fermented foods, certain vinegars, and even some ripe fruits contain small amounts. Cigarette smoke is another source. While alcohol is by far the largest contributor, people with ALDH2 deficiency process all sources of acetaldehyde less efficiently. Some nutritional supplements have been explored as supportive strategies, but no supplement has been shown to meaningfully compensate for the enzyme deficiency in clinical settings.