Diethylene Glycol

Diethylene glycol (DEG) is a hygroscopic liquid used as a co-solvent in antifreeze and coolant formulations. It improves low-temperature flow properties and provides additional solubilization for the inhibitor package. In retail consumer coolants, DEG is present at minor concentrations (typically 1.5–5%) relative to the primary ethylene glycol base. DEG has low acute toxicity at the concentrations used in automotive coolants. At higher doses, DEG follows a similar metabolic pathway to ethylene glycol, producing toxic metabolites that affect kidney function. Historical DEG poisoning events involved pharmaceutical adulteration (e.g., acetaminophen syrup contaminated with DEG in place of glycerin) at much higher concentrations than encountered in automotive use. At 1.5–5% in coolant, the primary contributor to the H302 mixture classification is ethylene glycol, not DEG.