I have zero worries about DMSO. I have used it for 6 months on a knee along with magnesium added to the DMSO. I use this ebay seller___ http://www.ebay.com/itm/DMSO-Dimethyl-Sulfoxide-99-99-Pharma-Grade-One-Gallon-Glass-Jug-Odorless-/161071400784?pt=LH_DefaultDomain_0&hash=item25809a8750
Add mag chloride or mag sulfate (epsom salts) to the DMSO which (in any event) needs 10-20% pure water added to it for best results. It is very desiccating. Draws water out of tissues. Dip your thumb in 99+++% DMSO for 20 mintes and you will find out what I mean
You will find internet references that 20% of DMSO will convert to MSM as it reaches the joint or other problem. I hope this is true. Dr Jacobs the DMSO pioneer sells MSM and DMSO at this site. MSM acting like Glucosamine Sulfate to heal joints and cartilage
I hope you are very judicious about your magnesium use as well. A few years ago I read about a young man who killed himself accidentally by using Epsom salts as a gargle, against halitosis, every day for over a month.
While typically, magnesium is flushed out of the system fast enough, gargling gradually increased his magnesium level until one day he had severe muscle cramps, and went to the hospital, and two days after that he was dead.
A similar phenomenon might possibly take place with using a DMSO + magnesium combination too frequently. If that is the case, the condition is called Hypermagnesemia.
http://en.wikipedia.org/wiki/Hypermagnesemia