Oral Allergy Syndrome

The oral allergy syndrome (OAS) is caused by 'cross-reactivity' between proteins found in fresh foods (fruit, vegetables and nuts) and pollen (usually birch and grass pollen in the UK).
 
The OAS is more common among teenagers and adults, but can develop in early childhood. The OAS develops subsequent to the development of pollen sensitisation, hence the tolerance of these foods when younger. This is unlike a 'classic' food allergy, which develops independent of pollen allergy.
 
 
Herewith an explanation of this syndrome as information on this condition is sometimes hard to come by:
 
The responsible proteins in the food (fruits and/or vegetables and/or nuts) that cause the OAS symptoms are 'heat-labile' and are therefore easily destroyed by cooking, freezing or processing of food. This explains why, generally, OAS is absent when food is consumed in its cooked, or processed form, for example apple pie and apple juice. 
 
Furthermore, as the majority of the responsible allergens reside in the peel of the fruit, many individuals with OAS will tolerate the fruit when eaten peeled.  

 

What Symptoms occur with OAS?

Most people with OAS experience mild to moderate intra-oral symptoms, such as a 'metallic' taste, itching, burning and tingling. Occasionally, swelling of the lips, mouth, face, tongue and throat may occur. Symptoms are usually short lived (a few minutes) and rarely progress to anything more serious. Occasionally, in highly-sensitive individuals, gut pain, vomiting, diarrhoea and/or a flare in eczema may be experienced even when the food is eaten cooked. 
 
Symptoms are usually more severe during the season in which the responsible pollen is at its height. The allergy specialist only rarely prescribes an injectable adrenaline device for use in the OAS.

 

What are the common food-pollen associations?

Patterns of pollen-food cross-reactivities have been described. For example, in the UK, birch pollen allergy is commonly associated with OAS reactions to apple, pear, cherry and even hazelnut. This does not mean that all birch allergic individuals experience symptoms of OAS to all of these foods. However, the number of foods causing reactions may increase with age. 
 
 
Cross reactions have been described for the follwinf foods. Importantly not all the foods listed below will cause reactions for any one individual:
 
  • Birch pollen (common in the UK), including hazelnut, apple, peach, pear, apricot, carrot, celery, cherry, chicory, coriander, fennel, fig, kiwifruit, nectarine, parsley, parsnip, pepper, plum, potato, prune, soy, wheat; Potential reaction: almond nut, and walnut
  • Alder pollen, including almond, apple, celery, cherry, hazel nut, peach, pear, parsley
  • Grass pollen (common in the UK), including fig, melon, tomato, orange
  • Mugwort pollen (more common in USA), including carrot, celery, coriander, fennel, parsley, pepper, sunflower
  • Ragweed pollen (common in the USA, and increasing in parts of Continental Europe), including banana, cantaloupe, cucumber, honey dew, watermelon, zucchini; Potential reaction: Dandelion or chamomile tea
  • Possible cross-reactions (to any of the above pollens), including berry (strawberry, blueberry, raspberry, etc), citrus (orange, lemon, etc), grape, mango, fig, peanut, pineapple, pomegranate, watermelon.
    imageImage below from UpToDate for Patients
Treatment:
 
  • Awareness and diagnosis of OAS
  • Avoidance of the offending food, but only in extreme cases 
  • Eating well-cooked, canned, pasteurized or frozen food, as these cause little or no reaction
  • Peeling food has shown to reduce the effects of the allergy in the throat and mouth, especially in the case of apples. These measures may not always help prevent/relieve symptoms in the gastrointestinal tract or skin for those who are highly-sensitive. 
  • Antihistamines may relieve the symptoms - especially during the pollen season
  • SLIT (Sub-lingual Allergy Immunotherapy) may improve OAS.
  • Rarely, persons with severe reactions may consider carrying injectable medication, such as an EpiPen, to bring relieve if necessary