Dr Amirah Khair, Dr Suzanne Dowling 

Ciaran is a 14 year old boy who presents to his GP with a complaint of having an itchy tongue and mild lip swelling when eating kiwi and melon, which lasts for a couple of hours. He is otherwise fit and well, except for hay fever, which is managed with oral antihistamines and a nasal spray. His mum is concerned that it is the beginning of a new food allergy and is asking if he will need an EpiPen.

The GP refers him to the Allergy Clinic. Ciaran and his mum have some questions, which you try your best to answer!

WHAT IS IT, DOCTOR?

Pollen-food syndrome (PFS), also referred to as oral allergy syndrome, is a hypersensitivity reaction triggered by raw fruit, vegetables, nuts or spices due to preceding pollen sensitization. Hence, it normally affects children and adults who have seasonal hay fever. Some people who do not have hay fever may still have PFS because they are still sensitised to pollen, but do mount an allergic reaction. However, these patients should also be flagged as it could also be suggestive of a primary food allergy. 

Common symptoms include itching, tingling and/or mild swelling of lips, tongue, inside of mouth, or throat, which usually occur within minutes of eating, and can last from minutes to hours.

Parents of younger children with PFS may even report them spitting out food and refusing them when being fed with the same food again.

Less common (<5%) and more severe systemic symptoms may include abdominal pain, nausea, vomiting and rarely, anaphylaxis. 

Note: if experiencing more severe systemic reactions, this must be differentiated from more serious forms of food allergies that are not pollen-related and be managed accordingly!

The table below lists common food culprits involved in PFS according to Allergy UK. It should be noted that reactions can be isolated to a single fruit listed below, or involve multiple groups of foods. 

WHY DOES IT HAPPEN?

PFS is an IgE-mediated type I immediate hypersensitivity reaction induced by sensitization to tree, grass or weed pollen. The pollen sensitization results in a cross-reaction with proteins in the food allergens listed above, due to the similar structure of the proteins found in both pollen and food allergens. As a result of this similar structure, when the offending food is eaten, pollen-specific IgE antibodies are able to recognise and bind to their proteins, forming an IgE-allergen complex that kickstarts localised release of inflammatory mediators, including histamine, from mast cells resulting in the symptoms of PFS.

The most common pollen offender is birch pollen, as its major allergen component, Bet v 1, is highly cross-reactive to many plant foods such as apple, peach, cherry and hazelnut.

Pollen Food Syndrome (FPS) is distinct from a primary food allergy – the table below highlights key differences.

Luckily in most cases, these proteins are denatured when processed and digested in stomach acid; hence most symptoms reported tend to be confined to the mouth and throat. As these proteins are removed altogether by cooking or peeling raw fruit/vegetables*, a parent might also report that their child eating apple crumble or applesauce does not cause itchy lips/tongue, but an apple eaten directly from the fruit bowl does!

*A caveat to that is a small group of people who react to both raw and roasted nuts, therefore these groups of patients will need to be referred to an allergy specialist to exclude a true food allergy.

TOP TIPS!

As always, a good history is key when navigating the vast spectrum of symptoms these children and teenagers may present with and will keep you in an allergist’s good books when referring on!

———-

– What types of symptoms are experienced? Are they confined to the oropharynx, or systemic, or both?

– Do they have a history of hay fever or other food allergies?

– Do they tolerate cooked or peeled forms of the food?

– Are there other foods in the table above that they react to?

ARE THERE ANY TESTS, DOCTOR?

In addition to a thorough history and physical examination, most patients referred to the allergy clinic will undergo skin prick testing (SPT) to pollen to confirm pollen sensitization, especially in groups of patients who do not report symptoms of hay fever. Parents could also be asked to bring in fresh samples of the offending foods to be used for SPT in clinic. It is both a quick and inexpensive test.

As a refresher, skin prick testing is when a drop of allergen extract is placed on the surface of the skin (commonly the inside of the arm or the back), and then pricked to introduce it to the top layer of the skin.

Image: NHS UK Food Allergy Diagnosis

A positive result, which is an itchy bump and surrounding redness (wheal) that develops within 10 minutes, means there is specific IgE antibody towards the allergen tested.* 

A positive test means the patient is sensitised but may not have an allergy in real life. Sensitisation plus a history of a reaction confirms the diagnosis. Avoid a fishing expedition for potential triggers. Due to cross reactivity with pollen, patients may be sensitised, but not truly allergic, to a wide range of fruits and vegetables. These ‘false positives’ can lead to unnecessarily restricted diets.

* It is worth noting that interpretation of results vary in practice, and will need to be considered in conjunction with the history by a trained allergist. 

SO WHAT CAN WE DO?

So as long as the offending raw foods are avoided in the diet, these symptoms should not recur. As mentioned previously, most foods can be tolerated when cooked. Several groups of patients have also reported only reacting to specific varieties of fruits or vegetables, based on the amount of proteins across the cultivars. For example for the apple aficionados amongst you: being able to tolerate Pink Ladies, but not Granny Smiths

Patients should also avoid fresh raw juices and smoothies as these contain a high protein load and are associated with more serious reactions. Especially if prepared outside of the home kitchen, as there could be accidental cross-contamination with the offending fruits and veggies.  

It is however advised to completely avoid all forms of the food causing the reaction if the child already has a confirmed food allergy (ie. allergy to peanuts) or if it has caused any severe systemic reactions, such as breathing difficulties and anaphylaxis. Hence, it is always worth safety-netting parents about the red flag symptoms of severe allergic reactions and anaphylaxis and knowing when to seek urgent medical attention. 

The good news is the majority of people with PFS only experience mild symptoms, which resolve within an hour or two without any treatment. Should the child accidentally be exposed to a fruit at a summer BBQ, however, they can be advised to drink lots of water and take an antihistamine if symptoms persist. 

Some parents will also ask if an adrenaline auto-injector (AAI) is needed. Most children with PFS will not need to carry around AAI with them, but this will ultimately be a decision based on the input of the specialist allergy team. 

ANY OTHER CONSIDERATIONS?

Remember to take a full dietary history. For most patients, avoiding a few fruits and vegetables will not have a large impact on their lives. Vegetarian and vegan patients, however, may be at risk of nutritional deficiencies if they have to exclude a wide range of fruits, vegetables and nuts. In addition, the process of cooking fruits and vegetables means some vitamins will be lost. Consult with a friendly allergy dietician for advice if multiple foods are restricted, particularly in the groups of patients mentioned. 

WILL THAT BE ALL?

In summary, you can tell Ciaran and his mother that his symptoms are highly suggestive of Pollen Food Syndrome. As Ciaran suffers from hay fever, it is likely that the mild symptoms he is experiencing is due to the pollen found in kiwi and melon, which are similar to the tree pollen that makes him sneeze and eyes water in the springtime. You advise Ciaran that he should avoid eating raw kiwi and melon in future, but if heated he should be able to eat the fruits without a problem. 

KEY POINTS:

  • PFS is triggered by eating fresh, raw, uncooked fruit, vegetables and nuts
  • patients usually have hay fever
  • most only develop mild-moderate symptoms that will resolve within an hour and do not need adrenaline auto-injector pens
  • managed by avoiding the foods involved, but some people may tolerate peeled/cooked foods as the proteins are removed/broken down
  • if severe systemic allergic reactions occur, consider primary non-pollen food allergies or anaphylaxis and treat accordingly

Sources:

  1. Allergy UK 2017, Oral allergy syndrome or pollen-food syndrome [Fact sheet] 
  2. Hunter H 2018, Pollen food syndrome, British Dietetic Association 
  3. Price, Alexandra MS et al; Oral Allergy Syndrome (Pollen-Food Allergy Syndrome), Dermatitis: March/April 2015 – Volume 26 – Issue 2 

Dr Amirah Khair, Paediatric ST2, RLH General Paediatrics and Allergy. Supervisor: Dr Suzanne Dowling 

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