Propylene glycol is much different than ethylene glycol. The term glycol actually refers to organic chemical structures that contain twin hydroxyl groups on neighboring carbon atoms. This common functional group is present in many different kinds of molecules. For example, all food carbohydrates contain glycol groups. Ethylene glycol is a toxic glycol used extensively in aqueous cooling systems (such as automotive antifreeze to prevent freezing in cold weather). Propylene glycol is very different, containing an extra carbon atom in its chemical structure that dramatically changes its chemical and biological properties. Unlike ethylene glycol, propylene glycol is safe for use in both topical and internally-consumed products.