Do you get an itchy mouth when eating an apple? Itchy hands when peeling potatoes? An upset stomach when drinking soya milk? Lip and tongue-tingling when eating peanuts? Then you may have pollen food syndrome!
What is pollen food syndrome?
Pollen food syndrome – previously known as oral allergy syndrome – affects around 2% of the UK population. That may not sound like a lot, but that actually makes it the most frequent food allergy for UK adults!
Pollen food syndrome (PFS) is what we call a cross-reactive allergy and is linked to hay fever.
This means that individuals with hay fever (meaning they are already allergic to pollen) can have similar reactions to certain types of foods as they do to certain types of pollen.
One common example of this is where an individual’s immune system mistakenly recognises an apple as if it were birch pollen. As a result, when this person eats an apple, they may get an allergic reaction in their mouth.
This cross-reactive allergic reaction happens because the protein structure in apples resembles that of birch pollen, so your body mistakenly thinks it is encountering birch pollen.
Apple-birch cross-reactivity is by no means the only example of PFS, as we will see.
What symptoms are associated with it?
Typically someone having a PFS reaction will experience a tingling, itching or soreness in the mouth, throat and ears and may get mild swelling of the lips. Some people even get abdominal pain and nausea.
Symptoms usually occur within 5-15 minutes after eating raw (uncooked) plant foods (although some people react to roasted nuts).
The reason why uncooked/raw foods create a reaction, while cooked foods normally do not, is because the process of cooking (heating up) typically changes the protein structure of foods. In such cases, the body no longer reacts to the food in an allergic way because its proteins no longer closely resemble that of the pollen to which that person is allergic.
What foods are involved?
PFS varies from person to person and depends entirely on the specific pollen allergy that person may have.
Those allergic to birch pollen typically react to:
Soya milk affects around 10% of birch-allergic individuals and can provoke more severe reactions.
Those allergic to grass pollen typically react to:
- swiss chard
The list goes on and is individual to each person!
For example, a person with birch pollen allergy may only get an itchy mouth with almonds but not with apples. Another person with birch pollen allergy will react to apples but not almonds.
Diagnosing Pollen Food Syndrome
Recent UK guidelines state that PFS should be diagnosed from an individual’s symptoms and history alone.
A PFS diagnosis means that a person meets all of the following 5 criteria:
- Have symptoms with raw fruit/nuts/carrot/celery
- The foods are tolerated when cooked
- The symptoms experienced occur quickly after eating
- The symptoms are situated in the mouth and throat
- They have seasonal hayfever or have positive allergy test results to pollen.
Testing can be helpful to establish which pollens are causing a problem. If you have more severe reactions to fruits and vegetables then it is important that allergy testing is undertaken.
Testing can also be an important means of distinguishing PFS from primary allergies.
Many people have been told they are allergic to peanuts, almonds and hazelnuts due to positive allergy tests, despite only getting mild oral symptoms when they eat them. In some cases, these individuals may only have PFS as opposed to a primary nut allergy. In such cases, further testing is important to avoid someone taking unnecessary levels of precaution, such as carrying an adrenaline pen.
With PFS, it is important to note that people should only avoid the specific foods which cause them symptoms, not the whole list of food types that match up with their pollen allergy.
Further good news is that heating the food destroys the offending protein structure. So even if you have reactions to the uncooked versions of certain foods, they can still be safely eaten in their cooked form, or even as tinned. Sometimes peeling or microwaving may be sufficient to prevent symptoms.
Of course, there are always exceptions and more severe reactions have been reported to foods like soy milk and soya protein isolate, which is now in lots of protein powders.
The most common nuts involved in PFS are hazelnuts, almonds, walnuts and brazil nuts. If you have symptoms to raw nuts you may be able to tolerate them roasted but some sensitive people may still react to them even in their roasted form.
There are also plant foods that do not provoke PFS, like cashews and pistachios, which can therefore be eaten safely.
So what is its relationship with gut symptoms?
A recent study showed that up to 50% of IBS patients have hayfever (much higher than the UK average) and that the people with IBS and PFS had more severe symptoms than those with IBS alone. This could mean that the dietary avoidance recommendations for PFS (as above) and allergy medications might be beneficial in reducing gut symptoms for those who are pollen allergic.
More research is needed!
This blog was authored by Aisling Phelan, an allergy specialist dietitian.
If you think you have symptoms of PFS then don’t suffer in silence – this is my specialist area and I’ll be happy to see you in my clinic – book here
Patel K, Vila-Nadal G, Shah J, Shamji MH, Swan L, Durham SR, Patel K, Skypala IJ. Is pollen-food syndrome a frequent comorbidity in adults with irritable bowel syndrome? Allergy. 2020 Jul;75(7):1780-1783. doi: 10.1111/all.14209. Epub 2020 Feb 14. PMID: 31999843.
Skypala IJ, Bull S, Deegan K, et al. The prevalence of PFS and prevalence and characteristics of reported food allergy: a survey of UK adults aged 18-75 incorporating a validated PFS diagnostic questionnaire. Clin Exp Allergy. 2013;43(8):928-940.