Fruit and vegetable allergy
Allergic reactions to fruit and vegetables are usually mild and often just affect the mouth, causing itching, a rash, or blisters where the food touches the lips and mouth. This is called oral allergy syndrome.
A number of people who react in this way to fruit or vegetables will also react to pollen from some trees and weeds. So, for example, people who are allergic to birch pollen are also likely to be allergic to apples.
Generally, cooking fruit and vegetables makes them less likely to cause an allergic reaction. Pasteurisation and other heat treatments (which are used, for example, on fruit juices) have the same effect. However, this is not the case for all fruit and vegetables. For example, cooking celery doesn't make it less likely to cause a reaction.
How ripe a fruit or vegetable is can also make a difference. For example, tomatoes are more likely to cause an allergic reaction the riper they are.