Sulfur mustard is a type of chemical warfare agent. These kinds of agents cause blistering of the skin and mucous membranes on contact. They are called vesicants or blistering agents. Sulfur mustard i...Sulfur mustard is a type of chemical warfare agent. These kinds of agents cause blistering of the skin and mucous membranes on contact. They are called vesicants or blistering agents. Sulfur mustard is also known as “mustard gas or mustard agent,” or by the military designations H, HD, and HT. Sulfur mustard sometimes smells like garlic, onions, or mustard and sometimes has no odor. It can be a vapor (the gaseous form of a liquid), an oily-textured liquid, or a solid.