Propylene glycol

Propylene glycol (1,2-propanediol) is a synthetic diol produced from propylene oxide, used extensively in food, pharmaceutical, and personal care applications as a humectant, solvent, and carrier. In food it retains moisture in products such as salad dressings, baked goods, and fillings, prevents crystallisation in certain syrups, and serves as a solvent to dissolve and carry flavour compounds, food colours, and extracts that are not water-soluble. Its relatively high polarity and low toxicity compared with ethylene glycol make it the standard food-grade diol for these applications.

JECFA evaluated propylene glycol in 1974 and established an ADI of 25 mg/kg body weight per day, a relatively high ADI reflecting the compound's low toxicity and efficient metabolism. Propylene glycol is metabolised in the liver to pyruvate and acetate — both normal cellular metabolic intermediates — and is subsequently oxidised through standard pathways. The kidney can also excrete unchanged propylene glycol efficiently, ensuring no accumulation in healthy individuals at dietary intake levels.

Propylene glycol is approved in the EU as E1520 for use in specific food applications at regulated maximum levels, with restrictions designed to limit total dietary exposure. The EU authorisation is more restricted than in the United States, where propylene glycol has GRAS status for broader food use. Key consumer considerations include the fact that propylene glycol can contribute to alcohol breath readings on some breathalyser devices at high intake levels, and that very large pharmaceutical doses (not food additive levels) have been associated with lactic acidosis in individuals with impaired metabolic clearance. At the low concentrations encountered in food as an additive, no adverse effects have been identified for the general healthy population.