What alcohol does

Ethanol is a small molecule, soluble in both water and fat, which is why it crosses membranes so easily and reaches every tissue in the body within minutes. There’s no organ it doesn’t get to. Almost all of it is then broken down in the liver, at a rate you have no way of influencing.

The liver breaks ethanol down in two stages. First, alcohol dehydrogenase converts it to acetaldehyde - which is considerably more toxic than the alcohol itself and is classified as a carcinogen. Second, aldehyde dehydrogenase converts acetaldehyde into harmless acetate.

The rate is fixed and can’t be hurried. Coffee, cold showers, food and exercise do nothing to speed it up - they may make you feel more alert while your blood alcohol is unchanged, which is arguably worse. A healthy liver clears roughly 7 to 10 grams of ethanol an hour, which is about one standard drink, and blood alcohol falls by roughly 15 to 17 mg per 100 ml of blood over that hour.

Age, sex, size and metabolism all move the figure, but body water content is the main variable - alcohol distributes through water, so the same drink in a smaller or leaner person produces a higher concentration. Enzyme levels vary genetically. And stomach contents matter: food doesn’t absorb alcohol, but it slows gastric emptying, so the same drink arrives at the bloodstream more gradually.

One genetic difference is worth knowing about by name. A variant of the ALDH2 gene, common in people of East Asian descent and uncommon elsewhere, produces a much less effective version of the second enzyme. Acetaldehyde accumulates instead of being cleared, which causes the facial flushing, rapid heartbeat and nausea known as alcohol flush reaction.

It’s often described as lacking the enzyme, which isn’t quite right - the enzyme is present and working badly, which is why the effect is a spectrum rather than a switch. Prevalence estimates vary by population and by study; commonly cited figures run from about 30% to 50% among East Asian populations, and closer to 8% worldwide. I have tried to be careful with the shorthand here, since "Asian" covers populations where the variant is barely present at all.

It isn’t only a cosmetic effect. Because acetaldehyde is a carcinogen, people with the variant who drink regularly carry a substantially elevated risk of oesophageal cancer. The flush is a warning signal, and I didn’t know that until I went looking.

The liver gets most of the attention because it does the processing, going from fatty liver through hepatitis to cirrhosis. But it isn’t the only organ affected. Heavy drinking causes vomiting and dehydration in the short run, and damage to the brain, the intestines and the pancreas over time. It reaches the whole body, not just the liver.

It’s also classified by the IARC as a Group 1 carcinogen, the same category as tobacco and asbestos, primarily through the acetaldehyde pathway described above.