I see my magician's allergy to orichalcum is already listed. Suffice it to say that someone isn't going to be committing high-end alchemy, or buying off-the-shelf weapons foci any time soon.

- Poultry, to add to your uncommon food allergies.
A nasty one though, as it affects which innoculations a person can receive.
- Red dye. In actuality, the woman who is allergic to this is allergic to insects, and most red food dye is made of crushed-up bugs. Yes, really. But "food dyes" is probably a broad enough category that it could be a common allergy.
FD&C Red 40 isn't cochineal (the "bug" in "bug juice" and at least one Snapple product), but it may be in your tattoo ink.
FD&C Yellow 5 (tartrazine) is harder to avoid: It's used in a couple of antibiotics, and it cross-reacts with sensitivities to aspirin, iboprofen, and the other common NSAIDs except for acetaminophen/paracetamol.
If you really want a miserable allergy: glucocorticoids (predisone, cortisone, etc.)
Bonus points if you recognize them as the primary medications for any allergic reaction short of anaphylactic shock.

Edit: Oh yeah, they're probably still used in preventing implant/organ rejection. Uncommon in practice, as usually it's asthma patients who get hit with the sensitivity IRL, but it would really suck to find out after having some augments done.