Mustard gas or sulfur mustard are names commonly used for the organosulfur chemical compound bis(2-chloroethyl) sulfide, which has the chemical structure S(CH2CH2Cl)2, as well as other species. In the wider sense, compounds with the substituents −SCH2CH2X or −N(CH2CH2X)2 are known as sulfur mustards or nitrogen mustards, respectively, where X = Cl or Br. Such compounds are potent alkylating agents, making mustard gas acutely and severely toxic. Mustard gas is a carcinogen. There is no preventive agent against mustard gas, with protection depending entirely on skin and airways protection, and no antidote exists for mustard poisoning.