World War One soldier with erythema of the chest, drawn five days after being exposed to mustard gas at Ypres, Belgium on 12th July 1917. 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.