Propylene glycol is a synthetic, colourless, odourless, tasteless liquid that belongs to the same chemical class as alcohol. It should not be confused with the toxic substance ethylene glycol.
Propylene glycol is commonly used as a food additive. It helps preserve moisture as well as dissolve colours and flavours. It is also used in some medications, cosmetic products, antifreeze and other industrial products. Propylene glycol is considered generally safe by US and European authorities. There is only one documented case of toxicity caused by excessive alcohol intake. It is recommended to limit intake to 11.4 mg per pound (25 mg/kg) of body weight per day.
Propylene glycol has very low toxicity. Poisoning rarely occurs, and it is typically due to high doses of medications that contain it. People with kidney or liver damage are not able to clear propylene glycol or lactic acid from the blood as effectively as healthy people. When receiving very high doses of it in medications, they have an increased risk of developing toxicity.
Young children and infants are not able to process propylene glycol as effectively as adults. Therefore, they are at risk of it building up in their bodies and developing symptoms of toxicity when exposed to high doses in medications. In vulnerable populations, high doses of propylene glycol from medications can cause problems with blood pressure and heart rate. However, there is no connection between heart problems and the amount of propylene glycol found in the diet.
At toxic levels, propylene glycol has been found to cause seizures and severe neurological symptoms. There have also been cases of nausea, vertigo and strange sensations. Between 0.8 and 3.5% of people are allergic to propylene glycol. Common symptoms include a rash on the face or body.