I don't have a problem with Cayenne itself. I love the stuff and have a high tollerance for it. But to actually use on top of a cankersore? That sounds like suicide.
I got it in my eye once, that was the worst.
I've found that Enchinaca directly on it numbs it. Just hard to keep away from my tongue because it burns the tip of it.
Oil is helping. I don't think it's actually making it go away, but it is soothing. When it starts acting up I just start swishing. Swishing is hard because my whole mouth is really messed up so half the time I don't swish, I just leave it in my cheek with air and let it sit there and it's still effective. It doesn't burn or sting, just soothes it.