DMSO is a solvent produced as a by-product of making wood pulp. It has been used medically for over 50 years and has a ton of awesome properties. Most notably, it's ability to carry large compounds through the skin. I have read that it is able to carry molecules with a molecular weight of less than a 1000 g/mol. Alone by itself it has a very low toxicity level and is generally considered safe for consumption if you were so inclined. It is also one of the strongest antioxidants available. The only thing that really stinks about it is the smell associated with it...garlic.
Read up on it!!
DMSO Toxicology Study
DMSO supposedly can carry <1000 g/mol
Alcohol i believe is around <300-500 g/mol
Plogel and some other carrier bases I believe go up to 800 g/mol but that may be under scrutiny.