Mustard agent, or sulphur mustard, commonly known as mustard gas, is a class of related cytotoxic and vesicant chemical warfare agents with the ability to form large blisters on the exposed skin and in the lungs. Pure sulfur mustards are colorless, viscous liquids at room temperature. When used in impure form, such as warfare agents, they are usually yellow-brown in color and have an odor resembling mustard plants, garlic, or horseradish, hence the name. Mustard agent was originally assigned the name LOST, after the scientists Wilhelm Lommel and Wilhelm Steinkopf, who developed a method for the large-scale production of mustard agent for the Imperial German Army in 1916.