Sulfur mustard, commonly known as mustard gas, was used as a chemical weapon in World War I and more recently in the Iran–Iraq War. Sulfur mustard is a vesicant alkylating agent with strong cytotoxic, mutagenic, and carcinogenic properties. After exposure, victims show skin irritations and blisters. This agent also causes respiratory tract lesions, bone marrow depression, and eye damage, the epithelial tissues of these organs being predominately affected. Inhalation of high doses of this gas causes lesions in the larynx, trachea, and large bronchi with inflammatory reactions and necrosis. The alkylating agent affects more the upper parts of the respiratory tract, and only intensely exposed victims showed signs like bronchiolitis obliterans in the distal part. Secondary effects of sulfur mustard exposure lead to chronic lung diseases such as chronic bronchitis.