Some people who are allergic or sensitive to certain pollens may also be sensitive to some foods. In some people, eating raw fruits and vegetables and some tree nuts can cause reactions such as swollen lips, itchy mouth, or scratchy throat. This is known as oral allergy syndrome and affects at least a third of all allergy sufferers. According to Dr. James Sublett of Family Allergy and Asthma in Louisville, Kentucky, "Produce and pollen contain similar proteins. Sometimes the immune system can't tell the difference."
If you think you have this problem, see an allergist. Shots or prescription meds may take care of the problem. And notice above it says raw fruits, etc. Cooking eliminates the problem.
Here are a few examples:
Allergic to Ragweed - You may have a problem with bananas, cucumbers, melons, kiwi, zucchini.
Allergic to Birch - You may have a problem with apples, almonds, carrots, celery, cherries, hazelnuts, kiwi, peaches, pears, and plums.
Allergic to Grass - You may have a problem with celery, melons, oranges, peaches, tomatoes.