well, think of pollen. say you're allergic to pollen, and you have a reaction that kills you. now switch you to the creature and pollen to the type. make sense now?
also, should the types be by element or species or other?
it would make sense if they were allergic to something else than their own species or type,
it would make sense if say water were allergic to fire, or if creatures were allergic to death, air or even life.
otherwise is an autoinmune desease, lol
anyways I guess it dont need to make sense, this is elements after all.