Alcohol kills cells through several simultaneous mechanisms: it physically disrupts cell membranes, generates toxic byproducts that damage DNA, and overwhelms cells with harmful free radicals. These aren’t separate possibilities. They happen together, compounding each other’s damage across every organ that alcohol touches.
Membrane Disruption: The First Point of Attack
Every cell in your body is wrapped in a thin membrane made of fat molecules arranged in two layers. This membrane controls what enters and exits the cell. Ethanol molecules are small enough to slip directly into this fatty barrier, and they do so quickly, penetrating through in roughly 200 nanoseconds. Once embedded, ethanol forms chemical bonds with the fat molecules in the membrane and physically shifts them toward the center of the barrier by about 0.2 nanometers. That sounds tiny, but at the molecular scale, it’s enough to loosen the entire structure.
The result is a membrane that becomes more fluid and more permeable than it should be. The internal scaffolding of the fat molecules, their hydrocarbon chains, becomes disordered. Think of it like loosening the weave of a fabric: substances that normally couldn’t pass through the membrane now can, and the cell loses its ability to regulate its own internal environment. This alone can be enough to kill a cell, but it’s only the beginning.
Acetaldehyde: The Toxic Byproduct
Your body doesn’t just absorb alcohol and leave it sitting around. It breaks ethanol down, primarily in the liver, and the first product of that breakdown is acetaldehyde, a compound far more dangerous than alcohol itself. Acetaldehyde is classified as a carcinogen, and the way it damages cells is direct and structural.
Acetaldehyde physically attaches itself to DNA, forming what scientists call adducts, essentially molecular scars on the genetic code. The most common of these is a stable modification on one of DNA’s building blocks, guanine. But the damage goes further. Two acetaldehyde molecules can combine and then react with guanine bases on opposite strands of the DNA double helix, creating crosslinks that fuse the two strands together. These crosslinks stall the machinery that copies DNA, block the reading of genes, and can cause double-strand breaks, one of the most dangerous forms of genetic damage a cell can sustain.
Acetaldehyde also creates crosslinks between DNA and the proteins that manage it, gumming up the works even further. When DNA damage accumulates beyond what a cell can repair, the cell either dies or, in a worse outcome, survives with mutations that can lead to uncontrolled growth. This is one of the primary ways alcohol causes cancer. The 2025 U.S. Surgeon General’s Advisory identified acetaldehyde-driven DNA damage as one of the best-established pathways linking alcohol to cancer risk.
Oxidative Stress and Free Radicals
The process of breaking down alcohol floods cells with an excess of high-energy electrons. Both steps of alcohol metabolism, converting ethanol to acetaldehyde and then acetaldehyde to acetate, feed electrons into your mitochondria, the energy-producing structures inside every cell. Normally, about 1 to 2 percent of electrons passing through mitochondria leak out and form reactive oxygen species (free radicals). Alcohol metabolism dramatically increases this leak by overloading the system with more electrons than it can handle efficiently.
On top of that, a liver enzyme called CYP2E1 that helps process ethanol is especially prone to generating free radicals on its own, including a particularly reactive species called the hydroxyethyl radical. Meanwhile, alcohol simultaneously weakens the cell’s antioxidant defenses, the cleanup crew that normally neutralizes free radicals. The result is a double hit: more free radicals being produced and fewer tools to contain them.
These free radicals attack cell membranes, proteins, and DNA indiscriminately. In the membrane, they trigger a chain reaction called lipid peroxidation that degrades the fatty barrier from the inside. In DNA, they cause the same kinds of strand breaks and mutations that acetaldehyde does. This oxidative stress also triggers inflammation through immune signaling molecules, which recruits immune cells that can cause additional collateral damage to surrounding tissue.
How Damaged Cells Actually Die
Alcohol-damaged cells die in two fundamentally different ways, and which one occurs matters for the surrounding tissue.
In apoptosis, the cell initiates its own controlled demolition. Immune signaling molecules activate receptors on the cell surface, which kick off a cascade of internal enzymes that methodically disassemble the cell from within. The cell shrinks, its contents stay contained, and neighboring cells absorb the debris cleanly. This tends to happen in earlier stages of alcohol-related damage.
In necrosis, the cell swells until its membrane ruptures, spilling its contents into the surrounding tissue. This triggers an inflammatory response as the immune system rushes to clean up the mess, and that inflammation damages nearby healthy cells. Necrosis is more common in later, more severe stages of alcohol injury.
The trigger point between these two fates often comes down to what happens in the mitochondria. When free radicals oxidize critical structures on the mitochondrial membrane, they can force open a pore called the mitochondrial permeability transition pore. Once this pore opens, the mitochondria release signaling molecules that push the cell toward death. Research in liver cell cultures has shown that alcohol exposure causes mitochondrial free radical production, loss of the electrical charge that powers the mitochondria, and release of the specific molecules that initiate apoptosis.
Cell Death Across Different Organs
Liver
The liver bears the heaviest burden because it handles most of the body’s alcohol metabolism. Cell death in the liver follows a recognizable progression. First, fat accumulates inside liver cells because alcohol metabolism disrupts normal fat processing (a stage called steatosis). As damage continues, immune signaling molecules and free radicals trigger cell death. In early stages, this is primarily apoptosis. In more advanced disease, such as alcoholic hepatitis, necrosis takes over, with cells swelling, bursting, and provoking waves of inflammation that lead to scarring (fibrosis), and eventually cirrhosis.
Brain
Alcohol damages brain cells through a somewhat different emphasis of the same basic mechanisms. During chronic exposure, the brain adapts to alcohol’s sedating effects by increasing the number of excitatory receptors on neurons. When alcohol is then withdrawn, these extra receptors become overstimulated by the brain’s normal excitatory signaling molecule, glutamate. The overstimulated receptors, which act as calcium channels, flood neurons with calcium ions. Excess calcium activates destructive enzymes and generates free radicals that degrade the neuron from within.
In the intact adult brain, current evidence points strongly toward oxidative stress and inflammatory signaling as the primary killers of neurons during chronic alcohol exposure. Immune-like cells in the brain release inflammatory molecules and damaging lipid compounds that create a toxic environment for surrounding neurons.
Gut Lining
The single layer of cells lining your intestine is particularly vulnerable. Alcohol kills these cells through the same combination of direct membrane damage, acetaldehyde-driven DNA injury, and oxidative stress. The consequences are visible: ulcerations, erosions, and loss of the cell layer, especially at the tips of the tiny finger-like projections (villi) that line the intestine. When these cells die, gaps open in the gut barrier. Bacteria and bacterial toxins that normally stay contained in the intestine leak into the bloodstream, triggering body-wide inflammation that compounds the damage alcohol is already doing to the liver and other organs.
How Much Alcohol It Takes
In laboratory studies, the concentration range considered equivalent to real-world human exposure is 10 to 100 millimoles per liter, with 25 millimoles per liter roughly matching a blood alcohol level of 0.08 percent (the legal driving limit in most U.S. states, reached after about 4 to 5 standard drinks). Above 100 millimoles per liter, alcohol becomes directly cytotoxic, meaning it kills cells through sheer chemical disruption regardless of the subtler metabolic pathways. But cell damage begins well below that threshold through the accumulated effects of acetaldehyde, free radicals, and membrane disruption.
Alcohol is also osmotically active, meaning it changes the concentration of dissolved substances in and around cells. This pulls water out of cells or forces it in, disrupting the delicate water and ion balance that cells need to function. This osmotic stress compounds the structural damage already happening at the membrane level.