Pollen Food Syndrome (aka Oral Allergy Syndrome)
The Oral Allergy Syndrome (OAS) / Pollen Food Syndrome (PFS) 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 summers (pollen-laden) seasons.
After initially tolerating foods such as tomatoes and stone fruit such as peaches and apples, children with OAS develop a dislike for these.
The syndrome gives rise to intraoral symptoms such as a fuzzy sensation, itching or tingling and, at worst, severe stomach pain, eczema flares or a slightly swollen lip or a hive around the mouth.
Anaphylaxis is very rarely associated, so an adrenaline-injectable device need not be carried for this condition.
The proteins that cross-react belong to protein families, such as profilins and pr-10 family proteins found in both grass and tree pollen. Therefore, pollen exposure and subsequent sensitisation give rise to this secondary form of food allergy.
These protein families are heat-labile, so they are usually tolerated when these foods are cooked. 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, and red moon apples) are better tolerated than white-fleshed apples (e.g. golden delicious apples) due to the variability in pr-10 family proteins therein. Grapes, watermelon (but not other melons) and berries (other than strawberries) also contain few cross-reactive pollen proteins, which are usually better tolerated.
Select nuts such as hazelnut, peanut, almond, and walnut also contain cross-reactive proteins and can cause symptoms of OAS when eaten, especially if the nuts are eaten unroasted.
Cashew and pistachio are low in these proteins and well tolerated (unless a primary allergy is present).
While immunotherapy to pollen is effective at treating grass and tree-induced allergic rhino conjunctivitis/hay fever, it is not always effective in treating oral allergy syndrome.
New-onset OAS can occur at any age but is typically only present in pollen-sensitised school-age children.
The most common pollen-provoking PFS is birch tree pollen; 66% of birch-sensitised UK adults and 48% of children have PFS.
The lengthening of the pollen season, the prevalence of more allergenic pollen due to rising temperatures, and the 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 access BSACI guideline, available online - https://onlinelibrary.wiley.com/doi/epdf/10.1111/cea.14208
