Here is a link to the Wiki page of OAS

http://en.wikipedia.org/wiki/Oral_allergy_syndrome

These same principles apply even more in our pets with multiple allergies. Pets have more histamine & inflammatory molecules stored in their skin. So, no matter what the source of the allergen, the first sign of an allergy flare up is itching & increased ear wax. Pets who are allergic to fleas, ticks or mites can develop oral allergy symptoms to these pests because they accidentally ingest them while grooming. Probably one of the many causes of eosinophilic mouth ulcers in cats.

More info; about people at Tree pollen allergy reacts with some foods.

Common Cross reactions:

Allergies to a specific pollen are usually associated with OAS reactions to other certain foods. For instance, an allergy to ragweed is associated with OAS reactions to banana, watermelon, cantaloupe, honeydew, zucchini, and cucumber. This does not mean that all sufferers of an allergy to ragweed will experience adverse effects from all or even any of these foods. Reactions may be associated with one type of food, with new reactions to other foods developing later. However, reaction to one or more foods in any given category does not necessarily mean a person is allergic to all foods in that group.

• Alder pollen: almonds, apples, celery, cherries, hazel nuts, peaches, pears, parsley, strawberry, raspberry
• Birch pollen: almonds, apples, apricots, avocados, bananas,^[10] carrots, celery, cherries, chicory,^[11] coriander, fennel, fig,^[12] hazel nuts, kiwifruit, nectarines, parsley, parsnips, peaches, pears, peppers, plums, potatoes, prunes, soy, strawberries, wheat; Potential: walnuts
• Grass pollen: fig,^[12] melons, tomatoes, oranges
• Mugwort pollen : carrots, celery, coriander, fennel, parsley, peppers, sunflower
• Ragweed pollen : banana, cantaloupe, cucumber, green pepper, paprika, sunflower seeds/oil, honeydew, watermelon, zucchini, echinacea, artichoke, dandelions, honey (if bees pollinate from wild flowers), hibiscus or chamomile tea
• Possible cross-reactions (to any of the above): berries (strawberries, blueberries, raspberries, etc), citrus (oranges, lemons, etc), grapes, mango, figs, peanut, pineapple, pomegranates, watermelon

 

How does one cope!  Knowing what you are allergic to helps because  you can avoid the foods that go hand in hand with pollen allergies.  Thorough cooking to breakdown the proteins in food into smaller bits can eliminate the allergic reaction. (Yes, fruit vegies and grains all have proteins or polypeptides) Cooking in water works the best to preserve the good elements in fruits and vegies, such as: poaching, stewing, baking in water until the food is really mushy like babyfood. Indian cuisine is well know for this method of cooking where any vegie becomes part of the sauce. Breaking down foods in acids like lemon, lime or vinegar can also work if allowed to marinate for hours to overnight.