Phosgene Oxime (CX), is a blister agent that operates similarly to the various types of mustard gas. It is a white crystalline powder which melts between 39 and 40° C and boils at 129° C. It has a high vapor pressure and has a highly irritating and unpleasant odor. It is, however, chemically unstable and decomposes quickly at high temperatures.
Phosgene affects the eyes, skin, and respiratory tract. It causes corneal lesions and eventually blindness, and when inhaled, causes pulmonary edema. It is highly destructive to human skin, causing irritation that is said to be highly similar to that of stinging nettles, but far worse. Even a few milligrams applied to the skin cause irritation, intense pain, and eventually a necrotizing wound. Few chemical compounds are known to be as destructive to human tissue.
Source: Federation of American Scientists website, resources on Chemical Warfare agents.