Oral allergy syndrome (pollen food allergy syndrome)

What it is

Oral allergy syndrome is generally considered a mild form of food allergy.¹ If you have hay fever from pollen, your mouth or throat may itch after you eat certain raw fruits or vegetables, because some proteins in these foods resemble pollen proteins.¹ The immune system can’t tell the two apart.³ AAAAI also calls it pollen food syndrome.¹ ACAAI uses the name pollen food allergy syndrome and says it is caused by cross-reacting allergens found in both pollen and raw fruits, vegetables or some tree nuts.²

People with the syndrome typically have an allergy to birch, ragweed or grass pollen.² It typically does not appear in young children.² It is more common in older children, teens and young adults who have eaten the fruit or vegetable for years without problems.²

Birch allergy is a large part of the picture: AAAAI says it happens in up to 50 to 75% of adults allergic to birch tree pollen.¹ Still, not everyone with a pollen allergy reacts to the linked foods.²

Symptoms

The most common symptoms are itching or swelling of the mouth, face, lips, tongue and throat.¹ They usually start right after eating the raw food, and in rare cases more than an hour later.¹ ACAAI describes an itchy mouth, a scratchy throat, and swelling of the lips, mouth, tongue and throat.² Itchy ears and hives on the mouth are sometimes reported.²

Symptoms usually stay in the mouth and fade quickly once the food is swallowed or removed.² Reactions beyond the mouth are rare, but they have been reported.² In one study cited by ACAAI, the syndrome progressed to symptoms elsewhere in the body in nearly 9% of patients and to anaphylactic shock in 1.7%.² AAAAI notes that, rarely, it causes throat swelling severe enough to make swallowing or breathing difficult.¹ Anaphylaxis from a pollen-linked raw fruit or vegetable is very uncommon.¹

Cooking is a useful clue. People with the syndrome can usually eat the same fruits or vegetables cooked, because heating distorts the proteins so the immune system no longer recognizes them.² High temperatures break down the proteins behind the syndrome, canned foods may cause less of a reaction, and the protein is often concentrated in the skin.¹ A reaction to cooked fruits or vegetables, or to nuts, is one of the reasons AAAAI gives for talking to a doctor.¹

What triggers it

The foods involved depend on the pollen. ACAAI lists these links:²

• Birch pollen: apple, almond, carrot, celery, cherry, hazelnut, kiwi, peach, pear and plum.²
• Grass pollen: celery, melons, oranges, peaches and tomato.²
• Ragweed pollen: banana, cucumber, melons, sunflower seeds and zucchini.²

AAAAI’s list is close but not the same. For birch it names pitted fruit or carrot, as well as peanuts, almond and hazelnut.¹ For grass it names peaches, celery, tomatoes, melons (cantaloupe, watermelon and honeydew) and oranges, and for ragweed it names banana, cucumber, melon and zucchini.¹ AAAAI says its list is not exhaustive.¹

AAFA’s birch list is longer: almond, anise or aniseed, apple, apricot, caraway, carrot, celery, cherry, coriander, fennel, hazelnut, kiwi, parsley, peach, peanut, pear, plum and soybean.³ For alder pollen, it lists almond, apple, celery, cherry, hazelnut, peach, pear and parsley.³

Reactions are personal. Some people report that only certain varieties of a fruit cause symptoms, such as specific apple varieties.¹

Season plays a part. The syndrome can happen at any time of year, but in many people it gets worse during the pollen season of the plant involved.¹ Across the US, trees produce the most pollen from February through April, and grass pollen is most common from April through early June.⁴ Weeds release pollen from August until the first hard frost.⁴

When to see an allergist

ACAAI advises seeing an allergist if you keep getting an itchy mouth after eating the same raw fruit or vegetable.² AAAAI suggests talking to a doctor if symptoms cause significant throat discomfort, get steadily worse, or come from cooked fruits and vegetables or from nuts.¹ The same goes for reactions elsewhere in the body after raw fruits or vegetables, such as hives, vomiting or trouble breathing.¹ If nuts make your mouth itch, AAAAI says to see an allergist.¹

There is no definitive test for the syndrome.¹ The diagnosis is made from your history of symptoms and, in some cases, skin prick tests and oral food challenges with the raw fruit or vegetable.² People with the syndrome often have a positive skin or blood test for the pollen involved.¹ After a reaction beyond the mouth to a fresh fruit or raw vegetable, ACAAI says that food could be considered a risk for anaphylaxis and advises consulting your allergist.² For how to handle reactions, talk to an allergist.

Some reactions are more serious. Throat swelling that makes it hard to swallow or breathe is rare, but it can happen.¹ Anaphylaxis is a serious reaction that comes on quickly and may cause death.²