In a sense, I can see what they are talking about as some chemicals can get through the skin and mess you up that way... but the most damage it can do is basically damaging that part of the skin and it really needs to get inside the body to truly maim.
If something doesn't need to breathe or bypass it, then it's a definitive problem.
He doesn't realize you are mocking him, that's why he's saying it again like you are joking.
I knew about that with TES, I didn't know about the damned robot though.