This white hydrophilic powder dissolves in cold water to form a clear viscous solution or gel depending on the concentration. It has a variety of trade names, but is generally applied as a thickener/emulsifier in both food and cosmetic products. Additionally, it can be used to treat constipation as it is not digestible, toxic, or an allergen. Methyl cellulose is not a naturally occurring substance, and is synthesized by heating cellulose with a caustic solution such as sodium hydroxide and then treating the resulting mixture with methyl chloride. As cellulose is also a polymer, different kinds of methyl cellulose can be prepared depending on which hydroxyl groups are substituted. Methyl cellulose is a primary ingredient in thickeners and emulsifiers, advanced cookery, artificial tears and saliva, personal lubricant, and mortar dry mixes. Methyl cellulose is also used in glue and binding applications, as well as cell cultures for the study of viral replication.