Why do some people flush when drinking alcohol

Whether at a dinner gathering with friends or chatting freely at a bar, alcohol often seems inseparable from social life. Yet we often notice a phenomenon: after a couple of drinks, some people’s faces turn red, while others do not. In some cases, redness even spreads across different parts of the body. Some explain that those who flush are “fast metabolizers” of alcohol, meaning their bodies are quickly breaking it down—a supposedly good sign. But what is the truth?

First, we need to understand what happens when our body takes in ethanol. Ethanol, the scientific name for alcohol, is the main component of alcoholic drinks. Once absorbed, ethanol enters the liver, where it is metabolized by an enzyme called alcohol dehydrogenase (ADH) into a toxic compound: acetaldehyde. Acetaldehyde is a Group 1 carcinogen that damages multiple systems in the body, causing dizziness, nausea, palpitations, blood vessel dilation, and facial flushing. It is also a major culprit behind cancers such as stomach and esophageal cancer. Next, acetaldehyde is further metabolized in the liver by another enzyme called aldehyde dehydrogenase (ALDH2) into harmless acetic acid. Eventually, this acetic acid is broken down into water and carbon dioxide, which are expelled from the body, or converted into fat for storage.

The key lies in ALDH2—the enzyme responsible for detoxifying acetaldehyde, often referred to as the “alcohol detox enzyme.” Some people have lower levels of ALDH2, or even lack it altogether. This means acetaldehyde breaks down more slowly, or not at all, leading to accumulation in the body. As acetaldehyde spreads through the bloodstream, one effect is dilation of facial blood vessels, causing flushing, and sometimes red patches across the body. This deficiency is especially common among Asians, which is why foreigners often call this phenomenon “Asian flush.” Therefore, when someone flushes easily after drinking, it usually indicates insufficient ALDH2 activity, meaning their body struggles to break down alcohol. They should be cautious with alcohol intake. If acetaldehyde cannot be properly metabolized and continues to accumulate, multiple problems arise: beyond flushing and dizziness, it can damage cellular and DNA systems, leading to various cancers. In extreme cases, excessive intake may cause acute poisoning, organ failure, shock, or even sudden death.

The amount of ALDH2 a person has is determined by genetics—it cannot be increased through diet or supplements. If you notice that you flush quickly after drinking, it is a sign that your body is not suited for heavy alcohol consumption, and avoiding alcohol is the safest choice. Even if you do not flush, moderation is still essential, because the body’s ability to metabolize alcohol has limits.