Pecans are classified as tree nuts and are in the top 14 allergens to be declared on food packaging in Europe.
There are 3 key allergens associated with pecan allergy, Car i 1, Car i 2 and Car i 4. They are all different types of seed storage proteins.
Car i 1 is a 2S albumin seed storage protein and is considered to be the main allergen linked to allergic reactions. This is why most nuts are grouped together for the purpose of labelling as sufferers of this allergy are most often allergic to multiple types of tree nuts, peanuts and seeds.
Car i 2 is a vicilin like protein also associated with seed storage.
Car i 4 is a Legumin seed storage protein.
Pecan allergy is not currently associated with any allergic syndromes.
Other food containing 2S albumin seed storage proteins are cashews, peanuts, brazil nuts, mustard seed, rapeseed, turnip, chickpeas, hazelnuts, pistachio, buckwheat, soya, sunflower seeds, walnuts, kiwi, castor beans and sesame seeds.
Other foods containing vicilin like proteins not mentioned in the list above are lupin, lentils, macadamia, peas and mung bean.
Almonds are the only other nut containing legumin proteins not mentioned in either of the above cross reactive lists. So if you are additionally allergic to almonds as well as pecans this may be the protein you are reacting to.