The proteins in birch pollen is identical to plum and people with birch pollen allergy may develop this allergy. People with a pollen allergy experiences oral allergy syndrome. The symptoms of this kind of allergy included itchy mouth, scratchy throat, hives, vomiting, abdominal pain, asthma, difficulty in breathing, anaphylaxis or swelling of the lips. Sometimes the immune system wrongly determines plum proteins as a threat and produces antibodies to detect them. This usually occurs due to cross reaction between foods due to birch pollen. Skin prick tests and other testing methods like blood test, oral food challenge and food elimination diet are used by allergist to test the kind of allergy.