Propylene glycol, also known as propane-1,2-diol and trimethyl glycol, may sound like some sort of fuel. The odorless and tasteless liquid is actually an organic compound. It’s the primary substance in antifreeze, but it’s also contained other things that you might use every day.

Though it’s a liquid, propylene glycol absorbs water. This makes it useful in medicines, cosmetics, and food products. You also can find it in:

  • toothpaste
  • deodorant
  • disinfecting gel
  • shaving cream
  • fragrances

Propylene Glycol in Food

Propylene glycol can be used as a food additive. It’s also used during food processing, for example, when extracting vanilla from vanilla beans. But its most common use is as a humectant. Humectants are substances that keep food moist to prolong shelf life.

Despite its abundance, propylene glycol’s use in food raises concerns. This is primarily because of what else it’s associated with. Propylene glycol is used to make antifreeze, airplane de-icing fluid, and brake fluids. It’s also used to make polyester and paints, and can even be found in fog machines and e-cigarettes.

When you look at it that way, propylene glycol sounds like something you’d prefer to keep in your garage, not your kitchen.

The U.S. Food and Drug Administration (FDA) has given propylene glycol a “generally recognized as safe” designation and the Agency for Toxic Substances and Disease Registry (ATSDR) gives it a “no cancer” classification. But the U.S. allows for higher concentration than the European Union. In 2014, batches of Fireball Whisky had to be recalled in Europe because of the concentration of propylene glycol it contained.

The World Health Organization says the acceptable dietary intake of propylene glycol is 25mg for every kilogram of body weight. The concentration of propylene glycol in U.S. foods can range from less than 0.001 percent (ex. eggs) and up to 15 percent (some seasonings and flavorings).

Studies in humans have shown that consuming 175-200 mg/kg of propylene glycol for 23 days showed no adverse effects.

When Does It Become Toxic?

While there’s no evidence that propylene glycol is unsafe, its cousin, ethylene glycol, is mildly toxic to humans. In large doses, ethylene glycol can cause seizures, renal failure, and other complications. This is because harmful crystals form as the body processes it. However, few cases of ethylene glycol poisoning have been reported. Those that have been reported involved rapidly infused intravenous injections of medications with high concentrations of the substance.

Propylene glycol, however, doesn’t create such crystals. It doesn’t appear to have any negative effects on your health, though the ATSDR notes that frequent skin exposure can irritate the skin. Some research also suggests that in high doses, it may contribute to cell death in the central nervous system.

Contact your local poison control center if you have accidentally ingested large amounts of propylene glycol.