Glycols are a class of organic compounds that contain two or more hydroxyl groups (-OH) on different carbon atoms. Commonly used glycols include ethylene glycol, propylene glycol, and butylene glycol. Synonyms for the word glycol include diol, diglycol, dihydric alcohol, and ethanediol. Ethylene glycol is widely used as a coolant and antifreeze, while propylene glycol is used as a solvent and vehicle for medications. Butylene glycol is commonly used in skincare products as a humectant to help retain moisture. Regardless of the specific glycol used, all are characterized by their ability to dissolve in water and their hygroscopic nature, making them useful in a variety of industries.