What is allergy cross-reactivity? 

Allergy cross-reactivity occurs when the body's immune system identifies the proteins in one substance (e.g., pollen) and the proteins in another (e.g., a fruit or vegetable) as being similar.1  When an individual comes into contact with either, whether or not it’s a protein in something that he or she is truly allergic to, the immune system can react in the same way, which in some cases can cause allergic symptoms.  


All that matters to the immune system is that the proteins are structurally similar or biologically related. If they are, cross-reactivity can occur. The risk of allergy cross-reactivity needs to be assessed by a healthcare professional, and important foods should never be removed from a diet without a confirmed diagnosis. The potential for cross-reactivity can make diagnosing specific allergies somewhat complicated.2

Symptoms that have manifested as a result of cross-reacting antibodies (i.e., proteins produced by the immune system to fight disease) cannot always be distinguished from those caused by genuine sensitization. However, by determining the primary sensitization, treatment or avoidance of symptoms can be effective. 

What is Pollen Food Allergy Syndrome (PFAS)? 


Pollen Food Allergy Syndrome (PFAS), also known as Oral Allergy Syndrome (OAS), is an allergic reaction that typically occurs after a patient who is sensitive to pollen eats certain foods, e.g., fruits, vegetables, nuts, and grains.3 PFAS is possibly the most common food allergy in adults, with up to 60 percent of patients allergic to pollen being affected.3  Additionally, up to 25 percent of children with allergic rhinitis (i.e., hay fever) also suffer from OAS. 4 

If you're sensitized to pollen, you may experience PFAS when certain foods touch your oral mucosa, lips, tongue, or throat. The symptoms of OAS appear within minutes of eating a raw form of the food but can last for hours. In the majority of cases, the responsible allergens are rapidly denatured by cooking and digestion, though certain patients can still present with systemic reactions.3  

Common PFAS or OAS symptoms include: 

  • Scratchy throat 
  • Itchy mouth or lips  
  • Swollen lips, tongue, or throat  

These symptoms could become worse during times of the year when pollen counts are high (usually in spring or fall).  

Common Allergy Cross-Reactivity Between Pollen and Foods

People with Oral Allergy Syndrome (OAS) typically have an allergy to birch trees, ragweed, or grass pollen.5 Foods that may cause OAS include tree nuts, soy, peanut, fruits, and vegetables.5

Pollen

Fruits

Vegetables

Nuts

Grains

Birch 

Kiwi, apple, pear, plum, peach, nectarine, apricot, cherry, banana, fig, avocado, strawberry, dried plum, mango 

Celery, carrot, parsnip, parsley, dill, cumin, cilantro, fennel, potato, tomato, pepper (green), chicory

Hazelnut, almond, walnut, peanut  

Soy, wheat, lentils, peas, beans 

Alder 

Apple, cherry, peach, pear, strawberry, raspberry

Celery, parsley

Hazelnut, almond, walnut 

 

 

Grass

Fig, melon, orange, kiwi, watermelon 

Tomato, potato 

Peanut 

Mugwort 

Mango 

Celery, carrot 

  

Ragweed

Banana,  watermelon, melon,  honeydew, cantaloupe 

Squash, pepper, cucumber, artichoke, hibiscus, zucchini,  chamomile  tea 

  

Sunflower seeds  

  
 

Other Cross-Reactivity Considerations

Cross-reactivity between shellfish:1 There is a high degree of cross-reactivity among crustacean shellfish (e.g., shrimp, lobster, crab, crawfish). The risk may be lower for cross-reactivity between crustacean shellfish and noncrustacean shellfish (mollusks) such as clams, oysters, scallops, and mussels. Of note, there is cross-reactivity between chitins (a component of the exoskeleton of shellfish and insects) in dust mites and crustacean shellfish in the form of a cross-reactive risk protein called tropomyosin. 

Cross-reactivity between latex and food:1 Approximately 30 to 70 percent of people with IgE-mediated allergies to latex can experience symptoms with any of several fruits cross-reactive to latex, including most commonly banana, avocado, kiwi, and chestnut. Several types of proteins have been identified to be involved in Latex-Fruit Syndrome.

Cross-reactivity between peanut and tree nuts or seeds: Peanut and tree nut allergies are often characterized by life-threatening anaphylactic reactions and lifelong persistence. While peanut allergy is more commonly seen in patients, many subjects develop a hypersensitivity to both peanuts and tree nuts.6 Although peanuts are actually legumes, approximately 20 to 30 percent of those with a peanut allergy are also allergic to one or more types of tree nuts.7  Additionally, walnut, pecan, and hazelnut comprise a group of strongly cross-reactive tree nuts. Hazelnut, cashew, Brazil nut, pistachio, and almond form another group of moderately cross-reactive tree nuts.8 

What is cross-contact? 

Cross-contact happens when a small amount of allergen gets into a food that it shouldn’t be in. Some food labels include “may contain” or “processed in the same facility as”  identifiers due to cross-contact. When it comes to food allergies, it’s important to understand the difference between cross-contact and cross-reactivity to avoid confusion and/or an unnecessary reaction. 

Find Answers 

Knowing if you’re allergic and what you’re allergic to can help you avoid or minimize symptoms when it comes to cross-reactivity and Pollen Food Allergy Syndrome. A blood test—together with an allergy-focused medical history—may help identify underlying allergen triggers. 

Learn more about blood testing for allergies.

   

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