Pollen Food Syndrome (aka Oral Allergy Syndrome)
The Oral Allergy Syndrome comes about due to cross-reactivity between pollens and food, it is an increasingly common but milder form of food allergy, usually coming on after having lived through 4-6 summer (pollen-laden) seasons.
Children with the OAS therefore, after having initially tolerated foods such as tomato and stone fruit such as peaches and apples, develop a dislike for these.
The syndrome gives rise to intraoral symptoms such as a fuzzy sensation, itching or tingling and at worse, stomach pain, eczema flares or a slightly swollen lip or a hive around the mouth.
Anaphylaxis is very rarely associated and so an adrenaline injectable device need not be carried for this condition.
The proteins that cross react belong to protein families such as profolins and pr-10 family proteins that are found in both grass pollen and tree pollen. It is therefore the pollen exposure, and subsequent sensitisation that gives rise to this secondary form of food allergy.
These proteins are heat-labile, so when these foods are cooked, they are usually tolerated, hence tomato sauce is tolerated but not uncooked tomato, the same will be true of peaches and pears. It also helps to remove the peel, as many of the allergens are concentrated in the peel but highly sensitive individuals will react to the pulp.
It may also be that red-fleshed apples (such as pink lady, kissable, red moon apples) are better tolerated than white fleshed apple (e.g. golden delicious apples) due to the variablit in pr-10 family proteins therein. Grapes, watermelon (but not other melons) and berries (other than strawberries) also contain few cross reactive pollen proteins and so are usually better tolerated.
Nuts such as hazelnut, peanut, almond and walnut do contain cross reactive proteins and can cause symptoms of the OAS when eaten, especially if the nuts are eaten unroasted; cashew and pistachio are low in these proteins and well tolerted (unles a priomar allergy to them is present).
Whilst immunotherapy therapy to pollen is effective at treating grass and tree induced allergic rhino conjunctivitis/hay fever, it is not always effective at treating the Oral Allergy Syndrome.
New-onset PFS can occur at any age, but usually presents in pollen-sensitised school-age children and adults with or without seasonal allergic rhinitis (SAR).
The most common pollen provoking PFS is birch tree pollen (Betula verrucosa); 66% of birch-sensitised UK adults and 48% of children have PFS. The lengthening of the pollen season, prevalence of more allergenic pollen due to rising temperatures, and increased severity of SAR all contribute to the growing prevalence of PFS in all ages.
For a detailed recent review on the OAS, please download our recent open acess BSACI guideline, available from - https://onlinelibrary.wiley.com/doi/epdf/10.1111/cea.14208