Allergies to Trees or Grasses can Result in Reactions to Food

When  people come to me because they think they may be allergic to certain foods, the first thing I ask is if they have an allergy to any trees or grasses. This may seem like a strange question but some people who are allergic to tree or grass pollen may have symptoms when eating certain foods because the pollen of the tree or grass is similar to the pollen that forms the fruit or vegetable and the body recognizes the similarity. This is known as cross-reactivity.

A person who is allergic to a tree or grass pollen reacts to the food — not because they are allergic to the food itself, but because they are allergic to a pollen from a tree or grass that has similar protein sequences. If a person has never been tested for environmental allergies (pollens, for example) or for food allergies, the first place I get started is to recommend that their doctor have them tested by an allergist. 

What is a Food Allergy?

An allergy is an immune-system mediated reaction which results in the body producing specific allergen IgE antibodies to the substance they are allergic to (the allergen). When people are exposed to the substance they are allergic to, the specific IgE antibody binds with their mast cells (a type of white blood cell that is part of the immune system) which result in the release histamine which causes the symptoms of an allergic reaction, which most often are sneezing, itching, difficulty breathing, or other symptoms. A true allergy is always involve IgE antibodies therefore food sensitivity tests based on IgG antibodies commonly performed by naturopaths do not diagnose food allergy.

Each IgE antibody is specific to one type of allergen, but some types of environmental substances (such as pollen or grass) or foods have several components that have protein sequences that can produce allergy. Using a food as an example, a person with a “milk allergy” may produce IgE antibodies to β-Lactoglobulin or α-Lactalbumin — two completely different proteins found in the whey fraction of milk, or they may be allergic to casein, a protein that makes up another fraction of milk.  A person with a milk allergy may produce specific IgE antibodies to α-Lactalbumin but not to β-Lactoglobulin, or to casein but not the others. Or, they may allergic to all three.

Similarly, a person allergic to a tree pollen may produce IgE antibodies to only one protein in that pollen, or to several.

Oral Allergy Syndrome (OAS) – pollen allergy

Most food allergies in adults who never had food allergies as children are the result of cross-reactions between food and inhaled allergens such as pollen[1] that they are allergic to. This is this known as Oral Allergy Syndrome (OAS). 

If a person has seasonal allergies in the early spring, it is most likely caused by allergies to tree pollen [2], and as many as 50%—70% of people who are allergic to birch pollen will have Oral Allergy Syndrome [3,4].

Alder is another common pollen allergen that results in OAS, as is latex found in rubber trees.

OAS reactions are most often thought of involving people’s lips, tongue or the roof of their mouth — where the cross-reacting food comes into contact with their body, but some people can also experience gastro-intestinal symptoms as a result of OAS — particularly related to birch pollen allergy[5].

It can get complicated, too.

An allergy to either birch or alder pollen can cause a Oral Allergy Syndrome to apples — but so can an allergy to apples, themselves.

How do we know if the person is reacting to apple because they are allergic to either birch or alder pollen (or both!), or because they are allergic to apples?

Only an allergist can determine that.

Since an allergist is specialized physician (MD), the costs of allergy tests done by an allergists are covered by provincial health plans

Once I’ve assessed someone, if I think they may be experiencing either food allergy of oral allergy syndrome, I will recommend that they speak to their doctor about being referred to an allergist for testing.

Once a person has been tested, the allergist’s office faxes me their report (with their permission, of course) and then person returns to me for teaching.  If they have tested positive to foods or to pollens, I teach them how to avoid coming into contact with foods they are allergic to, as well as which foods may result in cross-reactions because they are allergic to specific pollens.

If they have tested negative to food or pollen allergies and the person’s symptoms are gastro-intestinal (involving their stomach or intestines), then if they haven’t already been tested, the next thing I usually rule out is celiac disease (gluten intolerance). This is determined with a simple blood test that their family doctor can requisition.

If the person has no food or pollen allergies, doesn’t have celiac disease, and their doctor has ruled out inflammatory conditions such as Crohn’s or colitis, then very often they are diagnosed with Irritable Bowel Syndrome (IBS). Since symptoms of IBS can be significantly minimized with changes in diet, I provide them with this type of teaching.

Final Thoughts…

Spring is almost here, and if you have seasonal allergies and find yourself having more reactions to food, it may be an indication that you have Oral Allergy Syndrome.

More Info?

Under the Services tab, you can find out more information about the Food Sensitivity / Food Allergy Package and the Irritable Bowel Syndrome (IBS) Package and if you have questions, you can send me a note using the Contact Me form on this web page.

To your good health!


You can follow me on:



  1. Pong AH. Oral allergy syndrome. Vaughan (ON): Allergy/Asthma Information
    Association (AAIA); 2000. Available: /Articles/English
    /Oral_Food_Allergy.htm (accessed 2009 Dec. 3).
  2. Sussman G, Sussman A, Sussman D, Oral Allergy Syndrome, CMAJ 2010. DOI:10.1503/cmaj.090314
  3. Mogensen JE, Wimmer R, Larsen JN, et al. The major birch allergen, Bet v 1
    shows affinity for a broad spectrum of physiological ligands. J Biol Chem 2002;
    277: 23684-92.
  4. 8. Hoffmann-Sommergruber K, O’Riordain G, Ahorn H, et al. Molecular characterization of Dau c 1, the Bet v 1 homologous protein from carrot and its cross-reactivity with Bet and Api g 1. Clin Exp Allergy 1999; 29:840-7.
  5. Rentzos G, Lundberg V, Stotzer PO, Pullerits T, Telemo E. Intestinal allergic inflammation in birch pollen allergic patients in relation to pollen season, IgE sensitization profile and gastrointestinal symptoms. Clin Transl Allergy. 2014;4:19. Published 2014 May 30. doi:10.1186/2045-7022-4-19

Copyright ©2021 BetterByDesign Nutrition Ltd.

LEGAL NOTICE: The contents of this blog, including text, images and cited statistics as well as all other material contained here (the ”content”) are for information purposes only.  The content is not intended to be a substitute for professional advice, medical diagnosis and/or treatment and is not suitable for self-administration without the knowledge of your physician and regular monitoring by your physician. Do not disregard medical advice and always consult your physician with any questions you may have regarding a medical condition or before implementing anything  you have read or heard in our content.