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Oral Allergy Syndrome (OAS)

Updated: Aug 25, 2022

We all know that hay fever can strike at any time during the spring, summer or early fall seasons. Many longtime sufferers also know that they may experience an itchy mouth or throat after eating apples, celery or other food items during these seasons. Studies indicate that this occurs in up to 75% of adults who are allergic to springtime birch tree pollens and it is also widespread for other common seasonal allergies. This reaction occurs because the proteins found in some fruits and vegetables are very similar to those found in the seasonal pollen; the fruit or vegetable proteins confuse the immune system, creating an allergic reaction (cross-reactivity) to a substance other than what the immune system was sensitized. This cross-reactivity is usually called oral allergy syndrome but has also been termed pollen fruit syndrome (PFS).

What is Oral Allergy Syndrome?

OAS is a form of a contact allergic reaction that occurs upon exposure of the mouth and throat to raw fruits or vegetables. Symptoms typically include itchiness or swelling of the mouth, face, lip, tongue or throat, and occur immediately after eating raw fruits or vegetables. Although OAS is generally a mild form of food allergy, it can result in more severe throat swelling, leading to difficulty swallowing and/or breathing. Although uncommon, OAS can result in anaphylaxis for individuals who are highly sensitized to a given allergen.

One final note: If you’re allergic to these pollens but don’t have symptoms when eating related foods, you can still eat them. Individuals who experience severe OAS symptoms should talk to their allergist and potentially avoid these foods.

Depending on the pathway of sensitization, fruit or vegetable allergy is the result of a true primary food allergy or a secondary pollen-associated food allergy.

Primary Food Allergies

Primary food allergy often starts in infancy. Sensitization results from direct contact of the allergens with the gastrointestinal mucosa. This includes, above all, lipid transfer protein syndrome (LTP syndrome), which can trigger mild to severe systemic reactions and even anaphylaxis. These allergens are very stable to heat and retain their structure in the gastrointestinal tract, which is essential for the potential to sensitize and trigger allergic reactions.

Secondary Food Allergies

Secondary food allergy mainly affects older children, adolescents and adults who are diagnosed with pollen allergy and consequently react to cross-reactive food allergens in fruits. In pollen-fruit syndrome, the fruit allergy results from primary sensitization to labile pollen allergens, such as profilins and PR-10 proteins (Bet v 1 homologues). Symptoms are mild and consist of local reactions, such as oral allergy syndrome (OAS).

Common Oral Allergy Syndrome Cross-Reactions

For most cases of OAS, individuals react to different foods based on what type of seasonal allergies upon which they are sensitized. The primary pollens involved in OAS reactivities include birch, alder, ragweed, mugwort, Timothy grass and orchard grass. For example, individuals allergic to birch tree pollen may experience reactions to pitted fruits, carrots and various nuts. Similarly, individuals who are sensitized to grasses may have adverse reactions to peaches, celery, tomatoes, melons and oranges. Late summer allergies to ragweed can produce OAS symptoms to banana, cucumber, melon, and zucchini.

It should be noted that OAS symptoms to foods could actually be signs of a more severe allergic reaction. If there are any symptoms observed, the individual should see a board-certified allergist as soon as possible since nuts are more likely to cause serious allergic reactions which must be treated.

3 Ways to Help Avoid Oral Allergy Syndrome

Since OAS worsens during the pollen season of a given allergen, individuals demonstrating symptoms should avoid the consumption of associated raw foods. There are three ways to help avoid OAS:

  1. Cook food

  2. Eat canned food

  3. Peel fruits/vegetables

Interestingly, some level of cross-reaction can be reduced by cooking the offending food since it appears that high temperatures break down the proteins responsible for OAS. For example, a fresh apple may cause symptoms, but a person with OAS may be able to eat applesauce without symptoms. Similarly, eating canned food may also limit the reaction since pasteurization used in the canning process also denatures the offending protein. Finally, offending foods should be peeled before eating since allergic proteins are often concentrated in the fruit/vegetable skin.

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Available TREE allergy tests on NOVEOS:

Whole Allergen extract:

Gray Alder | Alnus incana | T002

Common Silver Birch | Betula verrucosa | T003

Hazelnut Tree | Corylus avellana | T004

American Beech | Fagus grandifolia | T005

Mountain Juniper | Juniper sabinoides | T006

Oak | Quercus alba | T007

Elm | Ulmus americana | T008

Olive Tree | Olea europaea | T009

Walnut | Juglans californica | T010

Maple Leaf Sycamore, London Plane | Platanus acerifolia | T011

Cottonwood Tree | Populus deltoides | T014

White Ash | Fraxinus americana | T015

Pecan, Hickory | Carya illinoinensis | T022

Mediterranean Cypress | Cupressus sempervirens | T023

European Ash | Fraxinus excelsior | T025

Acacia, Silver Wattle | Acacia dealbata | T026

White Birch | Betula populifolia | T030

White Hickory | Carya tomentosa | T041

Sycamore | Platanus occidentalis | T061

Virginia Live Oak | Quercus virginiana | T218

Allergen Components:

Bet v 1, PR-10, Birch | T215

Bet v 2, Profilin, Birch | T216

Bet v 4, Birch | T220

Bet v 2, Bet v 4, Birch | T221

Ole e 1, Olive | T224

Bet v 6, Birch | T225

NOVEOS Allergen Menu List, Specific IgE and Total IgE:

Download the latest product list of NOVEOS® Specific IgE Allergens and Total IgE, NOVEOS Assay Reagents, Consumables, and Supplies in the following languages:





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