Allergic reactions to fruit may be relatively mild and limited to the mouth and throat (itching of the lips, mouth, throat, and swelling of the lips, tongue, throat, and palate). This is called oral allergy syndrome. These mild reactions may occur in people allergic to pollen e.g. birch pollen, when they eat certain fruits.
Cooking destroys the pollen related fruit allergens, and thus cooked fruits are often safe for people with pollen related fruit allergy.
Other reactions to fruit may be more severe for example peach allergy as found in Southern Europe. The peach allergen is heat stable and therefore also found in juice and other heated products.
Persons allergic to latex (found, for example in latex gloves) may also have allergic reactions to fruits like banana, avocado and kiwi. The reactions occur in 30-80 percent of latex allergic persons and are often severe.