The most common type of food allergy in adults is oral symptoms triggered by fruits and vegetables. This type of allergic reaction is called either Pollen Food Syndrome (PFS) or Oral Allergy Syndrome (OAS), and is caused by a sensitization to foods related to allergenic pollens. OAS is also sometimes referred to as a "class 2 food allergy."
If you have a runny nose during pollen season, you are more likely to develop OAS as an adult. Virtually all adults with OAS have a history of allergic rhinitis (runny nose) due to pollen allergies.
Symptoms of OAS may include:
- Itching or tingling of the mouth, tongue or lips
- Swelling of the mouth, tongue, and/or throat (angioedema)
- Increased eczema symptoms in patients with eczema
- Rarely: vomiting, stomach cramps, or diarrhea
- Very rarely: anaphylaxis
Often, people with OAS will react to certain raw fruits or vegetables but will be able to tolerate them when well-cooked. For example, your mouth may itch after eating a raw apple, but you will be able to eat applesauce. This is because some of the proteins that cause pollen-related reactions break down when heated.
Diagnosis of OAS relies on a history of reactions and allergy testing. Unlike other types of food allergy, a double-blind, placebo-controlled food challenge is often not helpful in diagnosing OAS. Because reactions vary depending on the freshness of the food, and the direct contact with the skin of the mouth and tongue, results may not be accurate. For example, a capsule of prepared apple may not cause a reaction even if you have a reaction to eating a raw apple.
Your doctor will ask about your history of immediate reactions after eating certain fruits or vegetables. She will also ask about your history of seasonal allergies, hay fever, or runny nose. To identify the specific pollens and foods that are causing your symptoms, your doctor may order skin-prick testing or RAST blood testing.
OAS is caused by a cross-reactivity between an inhaled pollen allergen and the proteins found in certain fruits and vegetables. While the pollen plant and the foods are not biologically related, the structures of their proteins are so similar that the body reacts to both.
The most common type of OAS in Northern Europe is birch pollen allergy. One study found that 70% of people with a birch pollen allergy also have some sort of OAS. Because birch pollen allergy is so common, it is the most widely studied of all OAS associations. People sensitized to birch pollen may have OAS symptoms when they eat the following foods (in order of frequency):
- Apple (80%)
- Hazelnut (59%)
- Nectarine/peach (51%)
- Kiwi (48%)
- Walnut (41%)
- Carrot (35%)
- Apricot (33%)
- Cherry (32%)
- Pear (32%)
- Almond (32%)
- Peanut (24%)
- Plum (24%)
- Tomato (21%)
- Potato (19%)
- Celery (16%)
- Soybean (14%)
Grass pollen allergies are associated with sensitivities to:
Ragweed allergies are associated with sensitivities to:
Mugwort allergies are associated with sensitivities to:
Treatment and Management
As with most food allergies, the main method of managing OAS is avoiding trigger foods. Some people may only need to avoid their triggers in their raw form.
You may find that your OAS symptoms are worse when pollen counts are high. During pollen season, you may need to avoid foods that you can tolerate at other times of the year. Talk to your doctor about taking antihistamines or other allergy medication to help control your allergic rhinitis symptoms.
There have been some studies of birch pollen and apple allergies that have found that people who receive immunotherapy for birch pollen allergy are later able to tolerate raw apples. These studies were small, however, and there have not been studies done on other specific pollen-food interactions in immunotherapy.
Most adults with OAS do not need to carry an epinephrine auto-injector (commonly referred to by the brand name Epi-Pen). However, some people do have reactions that are severe enough, or have the potential to be severe enough, that they should be prescribed an auto-injector. Talk to your doctor about the type and severity of your reactions to your trigger foods.
Katelaris, C.H. Food allergy and oral allergy or pollen-food syndrome. Current Opinion in Allergy and Clinical Immunology 2010, 10:246-251
Webber, CM, et al. Oral allergy syndrome: a clinical, diagnostic, and therapeutic challenge. Ann Allergy Asthma Immunol. 2010;104:101-108.