Acetaldehyde is the toxic chemical your body makes when it first breaks down alcohol; the enzyme ALDH2 normally converts it quickly into acetate, but when it builds up it causes facial flushing, nausea and a fast heartbeat.1, 2 The International Agency for Research on Cancer (IARC) classifies acetaldehyde from drinking as a cause of cancer in humans, and no supplement has been shown to clear it faster in people.3, 4
Key takeaways
- Your liver makes acetaldehyde from alcohol and clears most of it with ALDH2, an enzyme in the mitochondria, so blood levels are normally low.1
- IARC classifies "acetaldehyde associated with the consumption of alcoholic beverages" as carcinogenic to humans (Group 1); it binds to and damages DNA.3, 5
- About 36% of East Asians flush when they drink, mostly because of an ALDH2 variant, and drinkers with one copy had 3.7 to 18.1 times the odds of esophageal cancer in case-control studies.2
- A 2020 review found blood acetaldehyde wasn't significantly linked to hangover severity, while blood alcohol and slow alcohol clearance were.6
- Acetaldehyde is also the most abundant carcinogenic compound in tobacco smoke.7
What is acetaldehyde, in one sentence?
Acetaldehyde is a small, reactive chemical that forms when ethanol is broken down, in your liver or by microbes in your mouth, and during fermentation, when yeast turns sugar into alcohol.7, 8 In the body it's a short-lived step between alcohol and acetate, and trouble starts when it piles up.
How does your body make and clear acetaldehyde?
Your liver does both jobs. Alcohol dehydrogenase (ADH), with help from an enzyme called CYP2E1 in heavy drinkers, turns alcohol into acetaldehyde, and the mitochondrial enzyme ALDH2 oxidizes most of that into acetate. Under normal conditions, circulating acetaldehyde stays low.1
The liver isn't the only source. Microbes in your mouth turn alcohol in saliva into acetaldehyde, and the unhealthy mix of microbes typical of poor oral health may double that local production.8 Salivary acetaldehyde stays elevated for as long as alcohol is present in the blood and saliva.7 For the full pathway, see how the body processes alcohol.
What does acetaldehyde do in the body?
It reacts with things it shouldn't. Acetaldehyde binds to proteins, forming "adducts" that can stop them working,1 and it binds to and damages DNA, one way alcohol causes cancer according to the US Surgeon General's 2025 advisory.5 Over years of heavy drinking, the liver takes much of the damage; see what actually supports your liver.
When acetaldehyde builds up, you feel it: facial flushing, nausea and a racing heart.2 The alcohol-aversion drug disulfiram works by blocking ALDH, which is why drinking on it makes people feel ill.1
Does acetaldehyde cause hangovers? What's known and what's debated
It probably contributes, but it isn't "the cause." NIAAA lists acetaldehyde among hangover contributors, describing it as a toxic byproduct that can inflame several organs.9
The human data are mixed. A 2020 review of biomarker studies found blood alcohol and slow alcohol elimination were associated with worse hangovers, but the association with blood acetaldehyde was not significant.6 Pointing the other way, Asian Americans who carry the ALDH2 variant that slows acetaldehyde clearance reported more severe hangovers.10 Our explainer on what causes a hangover weighs the other factors.
Acetaldehyde, flushing and ALDH2 deficiency
About 36% of East Asians (Japanese, Chinese and Korean people) flush when they drink, mostly because of a variant called ALDH2*2, and at least 540 million people worldwide are ALDH2-deficient. The variant makes an inactive enzyme: two copies leave no detectable ALDH2 activity, and one copy cuts it more than 100-fold.2
The flush is a warning sign, not a cosmetic quirk, and no supplement makes drinking safer for people who flush. If you flush, the safest choice is to drink very little or not at all. More in our guide to Asian flush.
Is acetaldehyde a carcinogen? Acetaldehyde and cancer risk
Yes. IARC classifies acetaldehyde associated with drinking alcohol as carcinogenic to humans (Group 1).3
Some of the strongest evidence comes from genetics. Because people inherit the ALDH2 variant regardless of how they drink, it works like a natural experiment: in case-control studies from Japan and Taiwan, drinkers with one copy had 3.7 to 18.1 times the odds of esophageal cancer after accounting for alcohol intake.2 Two Finnish researchers argue this model "proves conclusively" that acetaldehyde causes upper digestive tract cancers.8
Much of the exposure is local: whenever alcohol is present, acetaldehyde reaches mutagenic levels in saliva and parts of the gut.7 The Surgeon General's advisory lists at least seven alcohol-linked cancers: breast, colorectal, esophageal, liver, mouth, throat and voice box.5
The good news: moderating alcohol and quitting smoking both markedly lower exposure.8 The US Dietary Guidelines' bottom line applies: "Consume less alcohol for better overall health."11
Can anything help clear acetaldehyde? DHM, L-cysteine and probiotics (unproven in people)
Your own ALDH2 does the clearing, and no supplement has been shown in good-quality human trials to speed it up. The reliable way to make less acetaldehyde is to drink less.
| Ingredient | Study | Model and route | Result |
|---|---|---|---|
| Dihydromyricetin (DHM) | Silva 202012 | Mice, injected | Blood acetaldehyde fell after an alcohol dose |
| DHM | Skotnicová 202013 | Rats, by mouth | No change in how fast alcohol was cleared; ALDH not measured |
| Hovenia dulcis extract (less than 1% DHM) | Kim 201714 | 26 men, by mouth | No difference in blood acetaldehyde vs placebo |
| Hovenia combination drinks | Lee 202415 | 25 adults, by mouth | Blood acetaldehyde was higher at 6 hours |
| L-cysteine | Eriksson 202016 | 19 men, by mouth | Reported benefits rest on correlational analysis; criticized by other researchers17 |
- DHM results depend on the route. Injection bypasses the gut, and swallowed DHM is poorly absorbed, with only about 4% reaching the bloodstream in rats.18 No published trial has tested DHM by itself on acetaldehyde in people (as of October 2026).4 More in how DHM works.
- Engineered probiotics. Some newer products contain bacteria engineered to break down acetaldehyde in the gut. The published efficacy evidence we found is a lab study in simulated gut fluid, run by the developer's own scientists; we found no published human trial showing such a product lowers blood acetaldehyde or changes how people feel after drinking (as of October 2026).19
Even if a product did lower acetaldehyde, it wouldn't make drinking safe: alcohol itself is a Group 1 carcinogen.3, 5
Where else does acetaldehyde come from? Smoking and food
Tobacco smoke. Acetaldehyde is its most abundant carcinogenic compound, and active smoking produces salivary acetaldehyde levels similar to those after drinking.7
The drink itself. In a German lab's survey of 1,555 alcoholic beverages, acetaldehyde was lowest in beer and highest in fortified wines:20
| Drink type | Average | Range found |
|---|---|---|
| Beer | 9 | 0–63 |
| Wine | 34 | 0–211 |
| Spirits | 66 | 0–1,159 |
| Fortified wine (such as sherry or port) | 118 | 12–800 |
For scale, a 5-oz glass of wine at the average level holds about 5 mg of acetaldehyde, while your body makes far more from the glass's 14 grams of alcohol.21 The survey's authors say the cancer role of acetaldehyde swallowed directly still needs confirming.20
Food. Acetaldehyde also forms in fermented foods and turns up in some other foods and drinks, including some labeled "non-alcoholic."8
What we don't know yet
- How much acetaldehyde contributes to hangovers, compared with alcohol itself, inflammation and poor sleep.6
- Whether any supplement meaningfully lowers acetaldehyde in people.4
- How much acetaldehyde swallowed in drinks adds to cancer risk, beyond what your body makes from the alcohol.20
Frequently asked questions
Does acetaldehyde cause hangovers?
It may contribute, but the evidence is mixed. NIAAA lists it among hangover contributors, yet a 2020 review found blood acetaldehyde wasn't significantly linked to hangover severity, unlike blood alcohol. People with the ALDH2 variant that slows its clearance do report worse hangovers.
How long does acetaldehyde stay in your body?
You keep making it for as long as you're breaking down alcohol. ALDH2 normally clears it quickly, so blood levels stay low, but in saliva it stays elevated as long as alcohol is in your blood, and two to three times higher in people with ALDH2 deficiency.
Can you speed up acetaldehyde breakdown?
There's no proven way to do it in people. DHM results in animals conflict depending on whether it was injected or swallowed, and trials of other ingredients are small and low quality. Drinking less is the only reliable way to make less acetaldehyde.
Is acetaldehyde a carcinogen?
Yes. IARC classifies acetaldehyde associated with drinking alcohol as carcinogenic to humans (Group 1). It damages DNA, and people with an ALDH2 variant who drink have a much higher risk of esophageal cancer.
Which drinks contain the most acetaldehyde?
In a survey of 1,555 drinks, fortified wines averaged the most (118 mg per liter), followed by spirits (66), wine (34) and beer (9). But your body makes far more acetaldehyde from the alcohol itself, so how much you drink matters more than what.
Sources
- Cederbaum AI. Alcohol metabolism. Clin Liver Dis. 2012;16(4):667-685. PubMed
- Brooks PJ, Enoch MA, Goldman D, Li TK, Yokoyama A. The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption. PLoS Med. 2009;6(3):e1000050. PubMed
- IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Personal Habits and Indoor Combustions (Consumption of Alcoholic Beverages). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 100E. International Agency for Research on Cancer; 2012. IARC
- Skinner SG, Matcha S, Davies DL. Therapeutic effects of dihydromyricetin on wholly alcohol-attributed conditions: a systematic review. Nutrients. 2026;18(14):2221. PubMed
- Office of the US Surgeon General. Alcohol and Cancer Risk: The US Surgeon General's Advisory. 2025. hhs.gov
- Mackus M, van de Loo AJ, Garssen J, Kraneveld AD, Scholey A, Verster JC. The role of alcohol metabolism in the pathology of alcohol hangover. J Clin Med. 2020;9(11):3421. PubMed
- Salaspuro M. Interactions of alcohol and tobacco in gastrointestinal cancer. J Gastroenterol Hepatol. 2012;27(Suppl 2):135-139. PubMed
- Nieminen MT, Salaspuro M. Local acetaldehyde: an essential role in alcohol-related upper gastrointestinal tract carcinogenesis. Cancers (Basel). 2018;10(1):11. PubMed
- NIAAA. Hangovers. Updated December 2025. niaaa.nih.gov
- Wall TL, Horn SM, Johnson ML, Smith TL, Carr LG. Hangover symptoms in Asian Americans with variations in the aldehyde dehydrogenase (ALDH2) gene. J Stud Alcohol. 2000;61(1):13-17. PubMed
- US Department of Agriculture; US Department of Health and Human Services. Dietary Guidelines for Americans, 2025–2030. Released January 7, 2026. PDF
- Silva J, Yu X, Moradian R, et al. Dihydromyricetin protects the liver via changes in lipid metabolism and enhanced ethanol metabolism. Alcohol Clin Exp Res. 2020;44(5):1046-1060. PubMed
- Skotnicová A, Boubínová G, Boštíková Z, et al. Does dihydromyricetin impact on alcohol metabolism. Physiol Res. 2020;69(Suppl 4):S573-S581. PubMed
- Kim H, Kim YJ, Jeong HY, et al. A standardized extract of the fruit of Hovenia dulcis alleviated alcohol-induced hangover in healthy subjects with heterozygous ALDH2: a randomized, controlled, crossover trial. J Ethnopharmacol. 2017;209:167-174. PubMed
- Lee KW, Xu G, Paik DH, et al. Clinical evaluation of Hovenia dulcis extract combinations for effective hangover relief in humans. Foods. 2024;13(24):4021. PubMed
- Eriksson CJP, Metsälä M, Möykkynen T, et al. L-cysteine containing vitamin supplement which prevents or alleviates alcohol-related hangover symptoms: nausea, headache, stress and anxiety. Alcohol Alcohol. 2020;55(6):660-666. PubMed
- Benson S, Scholey A, Verster JC. L-cysteine and the treatment of alcohol hangover: a commentary on Eriksson et al. (2020). Alcohol Alcohol. 2021;56(5):628-629. PubMed
- Liu L, Yin X, Wang X, Li X. Determination of dihydromyricetin in rat plasma by LC-MS/MS and its application to a pharmacokinetic study. Pharm Biol. 2017;55(1):657-662. PubMed
- Hassan-Casarez C, Ryan V, Shuster BM, Oliver JWK, Abbott ZD. Engineering a probiotic Bacillus subtilis for acetaldehyde removal: a hag locus integration to robustly express acetaldehyde dehydrogenase. PLoS One. 2024;19(11):e0312457. DOI
- Lachenmeier DW, Sohnius EM. The role of acetaldehyde outside ethanol metabolism in the carcinogenicity of alcoholic beverages: evidence from a large chemical survey. Food Chem Toxicol. 2008;46(8):2903-2911. PubMed
- National Institute on Alcohol Abuse and Alcoholism (NIAAA). What is a standard drink? Updated December 2025. niaaa.nih.gov
- Substance Abuse and Mental Health Services Administration (SAMHSA). SAMHSA's National Helpline. Accessed October 9, 2026. samhsa.gov
Published by Fuller Health, which makes After Party. This article is general information, not medical advice: talk to a doctor or pharmacist about your own health, medicines and drinking. Last reviewed October 9, 2026. How we research and write.