Polyethylene glycol is a polyether compound with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide or polyoxyethylene, depending on its molecular weight. The structure of PEG is commonly expressed as H−ₙ−OH.
Propylene glycol is a synthetic organic compound with the chemical formula C₃H₈O₂. It is a viscous, colorless liquid which is nearly odorless but possesses a faintly sweet taste. Chemically it is classed as a diol alcohol that is miscible with a broad range of solvents, including water, acetone, and chloroform.