Would it not be interesting for characters to have allergic reactions to things in-game, such as, say, stings of certain insects or certain kinds of food? This could be chosen to be either completely random or a specific allergy could be chosen at character creation. Of course, it might have interesting consequences if one were to be allergic to Enrikudai...
Possible symptoms of an allergic reaction could include the usual we find over there in RL. Or simply loss of control over your character, as it tries to escape, fighting ability severely dimminished (not to mention crafting, magic, etc.). Perhaps even death could be a consequence.
If allergies were to be implemented, they would of course be an extreme annoyance. However, it would cause players to have to make more careful, and sometimes unique, decisions for their characters.
Certain races could be allergic to different things than other races. Whether members of one race could be allergic to members of another entire race is another matter. Personally, I think it would be an excessively irritating burden. If a bit amusing.
Treating allergies would perhaps be to take some sort of special medicine to enable them to either survive contact with the item that induces an allergic reaction or simply go through an area that is full of that particular item. Other treatments could be used as well, although I personally am too lazy to think of any more.
Pros:
Realistic
Powerful characters with allergies have great weakness - diminsihing their power
Requires more deliberate decision-making skills
(Insert new pro here)
Cons:
Annoying hinderance
Really annoying hinderance
(Insert new con here)
Comments?