Oral allergy syndrome

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Oral allergy syndrome (Pollen-Food Allergy)

Oral allergy syndrome (OAS) is a type of food allergy classified by a cluster of allergic reactions in the mouth and throat in response to eating certain (usually fresh) fruits, nuts, and vegetables that typically develops in adults with hay fever.[1]

OAS is not a separate food allergy, but rather represents cross-reactivity between distant remnants of tree or weed pollen still found in certain fruits and vegetables. Therefore, OAS is only seen in people with seasonal pollen allergies, and mostly people who are allergic to tree pollen.[2] It is usually limited to ingestion of uncooked fruits or vegetables.[2]

Another term used for this syndrome is pollen-food allergy. In adults up to 60% of all food allergic reactions are due to cross-reactions between foods and inhalative allergens.[3]

OAS is a Type 1 or IgE-mediated hypersensitivity, which is sometimes called a "true allergy". The body's immune system produces IgE antibodies against pollen; in OAS, these antibodies also bind to (or cross-react with) other structurally similar proteins found in botanically related plants.

OAS can occur any time of the year but is most prevalent during the pollen season. Individuals with OAS usually develop symptoms within minutes of eating the food.[4]

Signs and symptoms

OAS sufferers may have any of a number of allergic reactions that usually occur very rapidly, within minutes of eating a trigger food. The most common reaction is an itching or burning sensation in the lips, mouth, ear canal, or pharynx. Sometimes other reactions can be triggered in the eyes, nose, and skin. Swelling of the lips, tongue, and uvula, and a sensation of tightness in the throat may be observed. If a sufferer swallows the food, and the allergen is not destroyed by the stomach acids, it is likely that there will be a reaction from histamine release later in the gastrointestinal tract. Vomiting, diarrhea, severe indigestion, or cramps may occur.[4] Rarely, OAS may be severe and present as wheezing, vomiting, hives, low blood pressure,[5] or anaphylaxis.[6]


OAS produces symptoms when an affected person eats certain fruits, vegetables, and nuts. Some individuals may only show allergy to one particular food, and others may show an allergic response to many foods.[7]

Individuals with an allergy to tree pollen may develop OAS to a variety of foods. While the tree pollen allergy has been worked out, the grass pollen is not well understood. Furthermore, some individuals have severe reactions to certain fruits and vegetables that do not fall into any particular allergy category. When tropical foods initiate OAS, allergy to latex may be the underlying cause.[8]

Because the allergenic proteins associated with OAS are usually destroyed by cooking, most reactions are caused by eating raw foods. The main exceptions to this are celery and nuts, which may cause reactions even after being cooked.[citation needed]

Cross reactions

Allergies to a specific pollen are usually associated with OAS reactions to other certain foods. For instance, an allergy to ragweed is associated with OAS reactions to banana, watermelon, cantaloupe, honeydew, zucchini, and cucumber. This does not mean that all sufferers of an allergy to ragweed will experience adverse effects from all or even any of these foods. Reactions may be associated with one type of food, with new reactions to other foods developing later. However, reaction to one or more foods in any given category does not necessarily mean a person is allergic to all foods in that group.[citation needed]


The patient typically already has a history of atopy and an atopic family history. Eczema, otolaryngeal symptoms of hay fever or asthma will often dominate leading to the food allergy being unsuspected. Often well-cooked, canned, pasteurized, or frozen food offenders cause little to no reaction due to denaturation of the cross-reacting proteins,[6] causing delay and confusion in diagnosis as the symptoms are elicited only to the raw or fully ripened fresh foods. Correct diagnosis of the allergen types involved is critical. OAS sufferers may be allergic to more than just pollen. Oral reactions to food are often mistakenly self-diagnosed by patients as caused by pesticides or other contaminants. Other reactions to food—such as lactose intolerance and intolerances which result from a patient being unable to metabolize naturally occurring chemicals (e.g., salicylates and proteins) in food—need to be distinguished from the systemic symptoms of OAS.[citation needed]


Many people are unaware that they have OAS. However, if swelling, tingling or pain develops while eating certain foods, then it is wise to see an allergy specialist. Before a diagnosis can be made, keep a food diary. This is important as the physician can then perform an allergy test. Before testing is started, a comprehensive history is obtained so that random testing is avoided. The diagnosis of OAS may involve skin prick tests, blood tests, patch tests or oral challenges. When OAS is suspected, the oral challenge test is ideal.[citation needed]


To confirm OAS, the suspected food is consumed in a normal way. The period of observation after ingestion and symptoms are recorded. If other factors such as combined foods are required, this is also replicated in the test. For example, if the individual always develops symptoms after eating followed by exercise, then this is replicated in the laboratory.[citation needed]


OAS must be managed in conjunction with the patient's other allergies, primarily the allergy to pollen. The symptom severity may wax and wane with the pollen levels. Published pollen counts and seasonal charts are useful but may be ineffective in cases of high wind or unusual weather, as pollen can travel hundreds of kilometers from other areas. In addition, patients are advised to avoid the triggering foods, particularly nuts. Peeling or cooking the foods has been shown to eliminate the effects of some allergens such as mal d 1 (apple), but not others such as celery or strawberry. In the case of foods such as hazelnut, which have more than one allergen, cooking may eliminate one allergen but not the other.[citation needed]

Antihistamines may also relieve the symptoms of the allergy by blocking the immune pathway. Persons with a history of severe anaphylactic reaction may carry an injectable emergency dose of epinephrine (such as an EpiPen). Oral steroids may also be helpful. Allergy immunotherapy has been reported to improve or cure OAS in some patients. Immunotherapy with extracts containing birch pollen may benefit OAS sufferers of apple or hazelnut related to birch pollen-allergens. Even so, the increase in the amount of apple/hazelnut tolerated was small (from 12.6 to 32.6 g apple), and as a result, a patient's management of OAS would be limited.[13]

See also


  1. "Oral Allergy Syndrome". Canadian Food Inspection Agency. January 2000. Archived from the original on 2012-02-26. Retrieved 2008-01-25.
  2. 2.0 2.1 Papadakis, Maxine A.; McPhee, Stephen J.; Rabow, Michael W. (2017-09-11). Current Medical Diagnosis and Treatment 2018, 57th Edition. McGraw Hill Professional. p. 885. ISBN 9781259861499.
  3. Werfel, Thomas (2008). "Food allergy". Journal der Deutschen Dermatologischen Gesellschaft. 6 (7): 573–583. doi:10.1111/j.1610-0387.2008.06778.x. PMID 18611176.
  4. 4.0 4.1 Pong, Anthony Ham (June 2000). "Oral Allergy Syndrome". Allergy/Asthma Information Association (AAIA) Newsletter.
  5. "Oral Allergy Syndrome". oralallergy.net. Archived from the original on 2012-10-05. Retrieved 2010-01-26.
  6. 6.0 6.1 More, D. (April 28, 2007). "Oral Allergy Syndrome". About.com. Archived from the original on 2008-03-08. Retrieved 2008-01-25.
  7. "OAS Food Allergens". Canadian Food Inspection Agency. Archived from the original on 2012-02-26. Retrieved 2010-01-26.
  8. "Oral Allergy Syndrome". Asthma and Allergy Foundation of America. Archived from the original on 2015-09-05. Retrieved 2015-05-26.
  9. "General Information for Banana". Informall. 18 Oct 2006. Archived from the original on 8 March 2018. Retrieved 27 Sep 2011.
  10. Cadot, P.; Kochuyt, A.-M.; Van Ree, R.; Ceuppens, J.L. (2003). "Oral Allergy Syndrome to Chicory Associated with Birch Pollen Allergy". International Archives of Allergy and Applied Immunology. 131 (1): 19–24. doi:10.1159/000070430. PMID 12759485. S2CID 42538679.
  11. 11.0 11.1 Antico, A.; Zoccatelli, G.; Marcotulli, C.; Curioni, A. (2003). "Oral Allergy Syndrome to Fig". International Archives of Allergy and Applied Immunology. 131 (2): 138–142. doi:10.1159/000070929. PMID 12811022. S2CID 19077935.
  12. 12.0 12.1 "It Might Be Your Allergies". Rush University Medical Center. Archived from the original on 2015-02-19. Retrieved 2021-07-20.
  13. Bucher, X.; Pichler, W. J.; Dahinden, C. A.; Helbling, A. (December 2004). "Effect of tree pollen specific, subcutaneous immunotherapy on the oral allergy syndrome to apple and hazelnut". Allergy. 59 (12): 1272–1276. doi:10.1111/j.1398-9995.2004.00626.x. PMID 15507095.