Is DMSO dimethyl sulfoxide dangerous?

Yes. Dimethyl sulfoxide is dangerous. It is a polar aprotic solvent and can transport compounds through the skin and body extremely well. It is an industrial chemical, and not approved for use on humans by the f.d.a. If you are going to use it topically, dilute it a lot and use with something like aloe vera, vit c, tart cherry juice, activated silica, or some antioxidant because dimethyl sulfoxide is an oxidant. Only use on extremely clean skin because any crap on there will get dissolved into bloodstream, muscle, fat, who knows - maybe even bone.