I like the idea of elves having a distinct weakness against iron, to the point where they're intensely scared of it and can't stand the touch of it.
My question is: Assuming the Elves are mostly like humans, just how extreme can the weakness to iron realistically be? I know some people are allergic to steel (I am slightly), but would it ever be so bad that it's painful to the touch? Would such an extreme reaction prevent them from eating normal food that contains iron compounds? Could this be possible in a humanoid species without drastically changing their basic physiology?
Ideally, I want a race of elves who normally look like pointy-eared humans, are able to pass themselves off as human with a decent disguise, and can interbreed with humans, with the exception that for most of them, touching solid iron or steel physically hurts. How might this be possible and what would the ramifications be?