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Summary
Some patients with seasonal allergic rhinitis or conjunctivitis will develop itch and irritation of the tongue, mouth and throat after ingestion of some fresh fruits and vegetables, known as Oral Allergy Syndrome.

Symptoms are due to cross-reactivity

The majority of patients are allergic to similar (cross-reactive) proteins common to some pollens and some foods, typically other plants like fruit, salad, vegetables and sometimes nuts. Thorough cooking often destroys these allergens, so that when the same food is cooked, it may be tolerated. Nonetheless there are exceptions to every rule, since not all the allergens are destroyed by heat or digestion in the stomach and bowel.

Symptoms may occasionally be serious

While it is generally a benign disorder, swelling of the mouth or tongue or even anaphylaxis may occasionally occur, particularly if a large amount of food allergen is consumed, followed by vigorous exercise. 

Prevalence

Oral allergy syndrome (OAS) seems to be more common in countries and regions where birch trees are more commonly present. In northern Europe for example, up to 40% of patients with pollen allergy are estimated to be affected.

Australian data

The only Australian data available is from the Australian Capital Territory in south-eastern Australia (where birch trees are commonly planted), presented in abstract form at the Australian Society for Clinical Immunology and Allergy meeting in 2007: OAS 2007 ASCIA Poster.pdf. Prospectively collected data from pre-consultation questionnaires were entered into a Microsoft Access database and analysed retrospectively. Between January 1996 and August 2007, 4801 patients (61.6% female) were diagnosed with active hay fever (allergic rhinitis). Over that period, complaints of OAS rose from 10 to 23% in those with hay fever. There was no difference in the age of patients with OAS compared to those without (mean age 34 years). OAS patients were more likely to be female (72%). OAS was the primary reason for consultation in less than 5% of affected patients. Further analysis showed that the increase in OAS could be accounted for by an increase referral rate for systemic food allergy (FA), since there was no significant change in OAS complaints in those with ay fever alone when these patients were removed from the analysis. This finding was unrelated to shifts in gender, age, residential address or number of hay fever patients evaluated each year. Most patients with oral allergy did NOT volunteer symptoms unless specifically asked. Only 10% of patients in this group had serious allergic reactions to fruit and vegetables, compared to much higher rates in some European studies.

Management

The mainstay of therapy is avoiding the food or cooking it well.  Patients who are unable to tolerate fruit or vegetables in an uncooked form are forced to rely on well-cooked food in conjunction with vitamin supplements. More severely affected patients may require advice from a specialist dietitian to reduce the risk of impaired nutrition. There is preliminary evidence that this condition is becoming increasingly common in adults, a not unexpected finding when one considers the recent rise in hay fever (allergic rhinitis). While it may seem logical that immunotherapy/desensitisation to switch off inhalant allergy might reduce the severity of oral allergy symptoms as well, the small trials published show conflicting evidence of some benefit, no benefit or even harm.

References

1. •Katelaris CH. Food allergy and oral allergy or pollen-food syndrome. Curr Opin Allergy Clin Immunol. 2010 Jun;10(3):246-51.
   

2. •Webber CM, England RW. Oral allergy syndrome: a clinical, diagnostic, and therapeutic challenge. Ann Allergy Asthma Immunol. 2010 Feb;104(2):101-8
   

3. •Yun J, Katelaris CH. Food allergy in adolescents and adults. Intern Med J. 2009 Jul;39(7):475-8.
   

4. •Egger M, Mutschlechner S, Wopfner N, Gadermaier G, Briza P, Ferreira F. Pollen-food syndromes associated with weed pollinosis: an update from the molecular point of view. Allergy. 2006 Apr;61(4):461-76.
   

5. •Sloane D, Sheffer A. Oral allergy syndrome. Allergy Asthma Proc. 2001; Sep-Oct;22(5):321-5.

Last reviewed April 2012