I saw the thread called Decay/Reactivity of DMSO and it was closed. Since the thread was inconclusive I have decided to share my results. After approximately 18 years my 99.9% DMSO has completely decayed. When this happens it will no longer crystallize in the refrigerator. It will lose all effectiveness for pain relief. One observation was that my cap had a crack causing some exposure to air, which could have led to oxidation and accelerated decay, yet there was no noticeable volume loss. I didn't use it much because it makes me itch like crazy and I never found the proper ratio of dilution to minimize itching and achieve pain relief. Not to mention I never seem to throw anything away. Not a bad shelf life, whatever happened. Anyone else have older DMSO that retained potency?