Dimethylsulfoxide (DMSO), a byproduct of the chemical solvent industry, was approved by the FDA to treat musculoskeletal disorders in horses and dogs more than 30 years ago. Today it is commonly used by horse owners and veterinarians to relieve swelling and inflammation. When used topically, it causes moderate to intense heat—a benefit in treating old injuries that are still swollen but firm and cold to the touch. However, many veterinarians argue that DMSO produces exactly the opposite effect you want when treating a recent injury. Initial treatment for bumps and traumas that are hot and swollen to the touch is cold therapy; hosing a swollen joint or ligament with cold water and icing the area is standard primary emergency care. Putting DMSO on a “fresh” injury increases the heat in that area and can actually increase inflammation.
DMSO can be irritating to horses, and some will stamp their feet and even rub and chew treated areas. DMSO should not be used on an open wound.