ORAL ALLERGY SYNDROME
The pollen food syndromes (PFS) occur when certain proteins in plant foods trigger allergic reactions because they are similar to proteins found in pollen (a condition known as cross-reactivity).
Most of these reactions occur in people who have hay-fever (or seasonal allergic rhinitis) because certain plant-based foods, like fresh fruits, nuts, and vegetables, share similar allergens with the pollen from trees, grass, or weeds that the patient is allergic to. These allergens are alike enough to trick the immune system into thinking they are the same, so it produces IgE antibodies, leading to allergic reactions to both the pollen and the foods (see what is an allergy). These reactions can range from mild to severe.
PFS is common, occurring in older children and adults. It affects up to 60-70% of adults with hay-fever who have a birch tree pollen allergy. Symptoms can occur at anytime in the year, but are more common during the pollen season.
Oral allergy syndrome (OAS) is a type of pollen food syndrome where symptoms mainly affect the mouth and throat and are milder than a typical immediate type food allergy (see food allergy brochure). It involves itchiness and/or swelling of the mouth and throat within seconds to minutes of eating the food, and usually goes away on its own within 30 minutes. In OAS, the allergens are destroyed by heating, therefore it is possible to tolerate a cooked or canned version of a fruit or vegetable but not the raw form. Removing the skin from fruits or vegetables , where most of the allergen is found, can also reduce the amount of allergen consumed and make it easier to tolerate those foods.
Other types of PFS, like LTP (lipid transfer protein) syndrome, can cause more serious symptoms including vomiting, chest tightness, difficulty breathing and loss of consciousness on exposure to a variety of fruit, vegetables, grains, peanut and nuts. Unlike the proteins in OAS, LTP’s can withstand heat, so reactions can be severe to both raw and cooked foods. Exercise can also worsen allergic reactions due to LTP.
Some common OA syndromes include the following:
- Patients allergic to birch pollen may react to one or more of hazelnut, almond, carrot, celery, apple, peach, pear, apricot, kiwi fruit and nectarine.
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Grass pollen allergic patients may react to one or more of melon, tomato, orange, peach and celery.
- Ragweed allergic patients may react to banana, cucumber, melon or zucchini.
- Latex allergic patients may react to avocado, banana, chestnut, kiwi or papaya.
It is important to note that no single patient will be allergic to all the above listed foods.
Diagnosis
This is usually based on the history of reproducible reactions occurring with the specific range of foods. If the diagnosis is unclear, or to check for other involved foods, skin prick tests (SPT), blood tests or oral food challenges may be necessary. PFS is best diagnosed by SPT with the fresh fruit and vegetables rather than the prepared extract; and component- resolved diagnostics blood tests are becoming more important in diagnosing cross-reactivity syndromes.
Treatment
Avoid trigger foods where possible. Patients with mild OAS may cook or peel fruits prior to eating and may not need to carry adrenaline autoinjectors. For patients with severe reactions, patients must strictly avoid all forms of the food and carry an adrenaline autoinjector.
A medical specialist with a special interest and skill in allergy might be able to help. See the list of health care professionals on the AFSA website.