DMSO is dimethyl sulfoxide.   It was a biggie back in the 80s for arthritis pain relief.  It is used as a prescription drug for treating bladder ulcers - ouch - I shudder to think how it's administered. 

Used off-label for arthritis, there does not seem to be any scientific evidence for efficacy, only anecdotal evidence.  

A friend had great results back then; I berated him, as the stuff he was buying was technical grade purchased from a farm supply.  He countered that it was 95% pure - in medicine and scientific work, that is absurd, as you don't know what the other 5% might be.  Pharmaceutical grade is 99.995%.  For reference, in one of our labs, we purchased water for $80 per liter, but it was ultra, ultra, ultra pure and came with a certificate of analysis.   

Due  to ongoing arthritis in my wrists, I recently ordered some in a roll-on bottle.  I tried it and found no effect after 3 days' use.  More important, I had stinging, irritation and redness where it was applied.  As I write this, I rolled some on my wrist and within 1 minute, the stinging appeared.  No more; I'll stick with Voltaren; not perfect, but it does not add skin problems.  Gotta go wash this stuff OFF !

Carey Mitchell