Mustard gas is a human-made chemical warfare agent that causes blistering of the skin and mucous membranes on contact. It is also known as sulfur mustard, mustard agent, or by the military designation "H" or "HD". Mustard gas can be clear to yellow or brown when it is in liquid or solid form, and sometimes smells like garlic, onions, or mustard, or it may have no perceivable odor. It can be a vapor (gas), an oily-textured liquid, or a solid, and is usually a liquid at room temperature. People can be exposed to sulfur mustard through skin contact, eye contact, or inhaling (breathing in) the sulfur mustard. Exposure to large doses of sulfur mustard may result in harmful health effects such as decreased red and white blood cells and platelets, leading to weakness, bleeding, and infections, diarrhea, difficulty breathing, eye irritation, eye swelling, eye pain, eye tearing, fever, hoarseness, nausea, pain at the site of exposure, runny nose, shortness of breath, sinus pain, skin itching, skin pain, skin redness, sneezing, temporary blindness, vomiting, and wheezing. Mustard gas is also a carcinogen and mutagen, and contact with the liquid or exposure to high vapor concentrations can cause severe eye burns and permanent eye damage. There is no prophylactic treatment against mustard gas, and treatment is symptomatic as there is no antidote for mustard poisoning.