I use yarn, and don't bother to boil it. Never had any isssshuuueesss other than, uh, can't rememmmmmbeerrrr.....
My thinking is that, first, I'm lazy.
Second, the tiny amount of yarn / cotton used in a wick can't have any appreciable amount of contaminent.
Third - especially with cotton balls or swabs, they're made for cosmetic / health uses, so are probably pretty clean to start with.
Fourth, I'm lazy.
