Like many other allergies to fresh fruits and vegetables, pear allergy can take two different forms. In the North of Europe, people with birch-pollen allergy can develop a pear allergy due to the similarity between a protein in birch that causes birch-pollen allergy and a pear protein. This is called the birch-fruit syndrome with symptoms generally appearing within 5-15 min after consuming raw pear and comprising local reactions in the mouth and throat with itching and inflammation (called oral allergy syndrome, OAS). The molecule, known as an allergen, involved in this kind of allergy does not survive cooking. Therefore, people who react to this allergen can tolerate cooked pear. Individuals often develop adverse reactions to other fruits including apple, apricot, cherry, melon, banana, nuts such as hazelnut, or vegetables such as celeriac (celery tuber) and carrot.
In Mediterranean countries, people with pear allergy do not have birch-pollen allergy. Instead they often have allergy to peach. Symptoms are more severe including generalised urticaria, abdominal pain, vomiting and life-threatening symptoms, sometimes in addition to the OAS. These individuals tend to have more frequent and severe reactions when fruits are eaten with the peel. They also tend to develop adverse reactions to other fruits including apple, peach, apricot, plum, cherry and nuts (such as hazelnut and walnut). The allergen that causes this kind of allergy is tough and the allergenicity survives in processed foods such as juices. As a result, individuals with this kind of allergy cannot eat even cooked pear.