Vesicant Chemical-Warfare Agents By James M Madsen, MD, MPH, U S.Army Medical Research Institute of Chemical Defense (USAMRICD) Reviewed / Revised Jan 2023 View Patient Education Pathophysiology Symptoms and Signs Diagnosis Treatment Vesicants are chemical-warfare agents that cause blistering (vesicles) and include Mustards, including sulfur mustard and nitrogen mustards Lewisite Phosgene oxime (technically an urticant and a corrosive agent rather than a vesicant, although it is classified as a vesicant) These agents also affect the respiratory tract: mustards are predominantly type 1 agents, which affect the large airways, phosgene oxime is a type 2 agent, which affects the lower airways and alveoli, and Lewisite is a mixed agent.