It is a fatty acid with a sulfur, "thia" substitution at the third carbon, and should not have a sulfurious reaction. I have heard of TTA giving some people mouth blisters, so perhaps there is some unknown mechanism of irritation.
It is not a burning at all, and it takes about three days for the rash to develop. Very poison-ivyish, raised nodes, insane itch.
I'll stick to oral.