DMSO is a liquid solvent containing 99% purity dimethyl sulfoxide to help reduce acute swelling due to trauma. DMSO is a natural substance derived from wood pulp. It is an easy-application version of this organosulfur compound that can be used topically on horses to aid in reducing inflammation or as a method of enhancing drug action. Because DMSO is easily absorbed and can carry other substances through the skin and deeper tissues and membranes, it must be used per the label and the instruction of a veterinarian.