Illustration showing ulceration of a soldier's trachea on the twelfth day after being gassed with mustard gas during the First World War. At the top, the tongue and trachea are inflamed. Mustard gas was used as a chemical warfare agent in the First World War. Exposure to mustard gas can cause coughing and shortness of breath in the short term. It also has long term effects such as mouth, throat and skin cancer as well as leukaemia. The use of chemical weapons in the First World resulted in 90,000 deaths and more than 1.3 million casualties. Published in An Atlas of Gas Poisoning, 1918.