Polyethylene glycol, commonly referred to as, PEG refers to an oligomer or polymer of ethylene oxide and water.

It is used as an inactive ingredient in the pharmaceutical and cosmetic industry as a solvent, plasticizer, surfactant, ointment and suppository base. It is non toxic at any reasonable level. It is a nonpolar while having a lot of hydroxyl functionality. This making it suitable for suspension of ingredients that require solubility in oils, and is used commonly for compatibility reasons.