Propylene Glycol in Food: Why It's Not the Same as Automotive Antifreeze

The word “antifreeze” appears in a lot of online discussions about propylene glycol. And yes, that connection is real. Propylene glycol is used in antifreeze products. But that framing skips a critical detail: it’s in some antifreeze products specifically because it’s the less toxic alternative to the stuff that kills pets and poisons people.

Here’s a more accurate comparison. Water is also used in antifreeze. Coolant systems are water-based. Nobody argues that water is dangerous because it appears in your radiator.

What Propylene Glycol Actually Is

Propylene glycol (PG) is a small, water-soluble organic compound with the chemical formula C3H8O2. The “glycol” in the name means it has two alcohol groups, which is also true of ethylene glycol (C2H6O2). That structural similarity is the source of most of the confusion.

They are not the same molecule. Ethylene glycol is oxidized in the liver to oxalic acid and other metabolites that form crystals in the kidneys. That’s what makes it acutely toxic. Propylene glycol follows a completely different metabolic path. Enzymes convert it first to pyruvaldehyde, then to pyruvate and lactate, the same metabolites your body produces when it burns carbohydrates. Your liver handles propylene glycol the same way it handles the end products of glucose metabolism.

The FDA classifies propylene glycol as GRAS (Generally Recognized As Safe) under 21 CFR 184.1666. JECFA, the joint FAO/WHO expert committee that evaluates food additives internationally, established an acceptable daily intake of 0-25 mg per kilogram of body weight. That’s a generous safety margin above the amounts found in food.

What It Does in Food

Propylene glycol earns its place on ingredient lists for two distinct reasons.

The first is moisture retention. As a humectant, PG binds water molecules. Think of it like a sponge that holds onto water even as the surrounding environment tries to dry the product out. This is why some packaged baked goods stay soft for weeks at room temperature. Without a humectant, the moisture in the crumb would migrate outward and the product would go stale within days.

The second is solvent activity. Many flavor compounds and food colorings are fat-soluble, meaning they don’t disperse evenly in water. Propylene glycol can dissolve these compounds and hold them in suspension, acting as a bridge between the fat-soluble flavor molecule and the water-based food matrix. That’s why you’ll find it listed in flavoring preparations and some beverage concentrates where the ingredient label reads something like “natural and artificial flavors (propylene glycol).”

You’ll find PG in flavored salad dressings, flavored beverages, some ice creams and soft-serve mixes, packaged baked goods, flavoring extracts, and some food colors. The quantities used are small. The humectant function typically requires 0.5-5% by weight. The solvent function uses even less.

The Antifreeze Story, Fully Explained

Conventional automotive antifreeze uses ethylene glycol as its main active ingredient. It lowers the freezing point of water dramatically and raises the boiling point. It works great. It’s also toxic enough that a small amount can kill a dog or a child, partly because it tastes sweet.

Propylene glycol also depresses the freezing point of water and raises the boiling point. It’s used in antifreeze formulations marketed as “pet-safe” or “RV antifreeze” because its toxicity is orders of magnitude lower. The mechanism is the same. The safety profile is completely different.

So when someone says “propylene glycol is in antifreeze, therefore it’s dangerous in food,” they’ve made a category error. The presence of a compound in an industrial product says nothing about that compound’s safety at food-use levels. Ethanol is in gasoline (as an octane booster). Nobody argues whiskey is a fuel additive. Citric acid is used in industrial cleaning products. It’s also in every lemon.

What the Safety Record Shows

Decades of toxicological data support PG’s safety in food. Long-term rat feeding studies found no adverse effects at dosing levels far above human dietary exposure (Gaunt et al., 1974). The EFSA conducted a full re-evaluation in 2018 and confirmed the existing ADI without revision.

There’s one real exception worth noting: cats. Cats lack certain liver enzymes that dogs and humans use to metabolize propylene glycol efficiently. In cats, PG can oxidize red blood cells and cause Heinz body anemia. The FDA specifically prohibits propylene glycol in cat food for this reason. This isn’t a safety concern for the people eating the food — it’s a pharmacological difference in feline metabolism.

There are also historical cases of propylene glycol toxicity in humans receiving it intravenously in large amounts, typically as a drug vehicle in ICU settings. Intravenous delivery at clinical doses is a completely different exposure scenario from eating a salad dressing that contains a fraction of a percent of PG. The clinical literature on IV toxicity doesn’t translate to dietary safety concerns.

Reading the Label

If you want to identify propylene glycol on a label, look for “propylene glycol” or “propylene glycol alginate” (a different compound made from PG and alginic acid, used as a stabilizer). In Europe it carries the E number E1520. It may also appear inside the ingredient declaration for “natural and artificial flavors” without being listed separately, since flavor compositions are considered trade secrets under FDA rules.

The practical reality is that propylene glycol at food-use levels isn’t a health concern for adults or children. The antifreeze comparison is vivid and shareable but doesn’t hold up to the basic chemistry. If you’re still uncomfortable with it, it’s not difficult to avoid — it shows up mainly in heavily processed flavored products, and label reading will catch most of it.

References appear at the bottom of this page. All cited studies link to PubMed or official regulatory sources.