Ethylene glycol is highly toxic to humans. As little as 100 milliliters, roughly three and a half ounces, can be lethal for an average adult. It’s the main ingredient in most automotive antifreeze, and its sweet taste makes accidental ingestion by children and pets a persistent concern. The danger doesn’t come from the chemical itself but from what your body turns it into.
Why Ethylene Glycol Is Dangerous
Ethylene glycol in its original form is relatively harmless. The real problem begins when your liver starts breaking it down. An enzyme called alcohol dehydrogenase (the same one that processes drinking alcohol) converts ethylene glycol into a series of increasingly harmful byproducts.
The first major byproduct is glycolic acid, which builds up in the blood and causes severe acidosis, a dangerous drop in blood pH that disrupts nearly every organ system. The second critical byproduct is oxalic acid, which binds to calcium in the blood and forms tiny crystals called calcium oxalate. These crystals lodge in the kidneys, physically blocking and destroying the delicate tubules that filter your blood. This leads to acute kidney failure. Along the way, the drop in blood calcium caused by oxalic acid can trigger muscle spasms, seizures, and dangerous heart rhythm changes.
Where You’ll Find It
Antifreeze is the most common source, and it contains ethylene glycol at concentrations around 95% by weight. But it shows up in a surprisingly wide range of products: hydraulic brake fluids, some stamp pad and ballpoint pen inks, paints (where it can make up 26 to 80% of the volatile compounds), de-icing solutions for aircraft, solvents, and even some cosmetics at concentrations up to 5%. It’s also used in manufacturing synthetic fibers and plastics.
The bright green or orange color of most antifreeze products is an added dye, not inherent to the chemical. Ethylene glycol itself is colorless and odorless, with a slightly sweet taste. This is what makes it particularly hazardous around children and animals, who may drink it willingly.
How Poisoning Progresses
Ethylene glycol poisoning unfolds in stages as the body metabolizes the chemical over hours. Understanding this timeline matters because early treatment, before the toxic byproducts accumulate, dramatically improves outcomes.
In the first few hours, the effects mimic alcohol intoxication: confusion, slurred speech, nausea, and vomiting. Someone who has ingested ethylene glycol may appear drunk but won’t smell like alcohol. This stage is deceptive because the person may not seem critically ill.
Between 12 and 24 hours, the metabolic byproducts start accumulating. Rapid breathing develops as the body tries to compensate for rising acid levels in the blood. Heart rate increases. In severe cases, the calcium depletion caused by oxalic acid can lead to muscle twitching, cramping, and cardiac complications.
By 24 to 72 hours, kidney damage becomes the dominant concern. Calcium oxalate crystals deposited in the kidney tubules cause widespread tissue death, primarily in the proximal tubules responsible for reabsorbing essential nutrients. Urine output drops. Without treatment, this can progress to complete kidney failure requiring dialysis.
How Much Is Dangerous
The estimated minimum lethal dose is about 1.6 grams per kilogram of body weight, which works out to roughly 100 milliliters (less than half a cup) for a 70-kilogram adult. Blood levels of just 20 milligrams per deciliter are considered the threshold for toxicity. To put that in practical terms, even a few swallows of undiluted antifreeze can push someone into the danger zone, and smaller amounts are proportionally more dangerous for children.
Survival depends heavily on how quickly treatment begins. People treated before significant metabolism occurs often recover fully. Those who present late, after kidney damage has set in, may need weeks or months of dialysis and can sustain permanent kidney injury.
How Poisoning Is Treated
The core strategy is simple: block the liver enzyme that converts ethylene glycol into its toxic byproducts. If the chemical can’t be metabolized, it stays in its relatively harmless original form and is eventually filtered out by the kidneys.
Two antidotes accomplish this. Fomepizole directly inhibits the enzyme, and it’s the preferred treatment in most hospitals because of its predictable dosing and fewer side effects. Ethanol (medical-grade drinking alcohol given intravenously) works as a competitive alternative, essentially keeping the enzyme busy so it can’t process the ethylene glycol. Ethanol is used when fomepizole isn’t available, but it requires careful monitoring since it causes intoxication.
In cases where significant amounts of ethylene glycol or its byproducts are already circulating, dialysis is used to physically remove them from the blood. This also addresses kidney damage that may have already begun.
Ethylene Glycol vs. Propylene Glycol
These two chemicals are often confused, and the distinction matters. Propylene glycol, found in “pet-safe” antifreeze products and many foods, is far less toxic. Your body metabolizes it into lactic acid and other compounds that are easily cleared. Ethylene glycol, by contrast, produces the cascade of toxic acids described above. If you’re choosing antifreeze for a household with children or pets, propylene glycol-based products carry significantly less risk in case of accidental exposure.