Sulfur mustard, commonly known as mustard gas, is a chemical warfare agent first used in World War I. It is a yellowish-brown liquid at room temperature and has a distinctive mustard-like odor. Sulfur mustard can cause severe skin blisters, respiratory damage, and long-term health issues upon exposure. This compound is classified as a chemical weapon and is banned under the Chemical Weapons Convention. Despite its name, sulfur mustard is not a gas but can form a vapor that is harmful when inhaled. Its use in warfare has led to significant international efforts to prevent its proliferation and use.