YSK: Pink peppercorns are actually a tree nut, and can cause allergic reactions.
Why YSK: Since they are not true peppercorns, but rather a tree nut in the cashew family, they have caused anaphylaxis in people even from kitchens where nut allergies are kept in mind and taken seriously. Since pink peppercorns are often included in peppercorn medleys and are often not labeled as containing nuts, it's possible to expose someone with a tree nut allergy without knowing.