We are in the midst of hayfever season. This typically spans March to September when all the tree and grass pollens are in the air. Many hayfever sufferers are allergic to one or more tree and grass pollens and this time of year can be particularly problematic for them.
So why do they have trouble eating apples?
There is a condition called Oral Allergy Syndrome (OAS) or Pollen-food syndrome (PFS) which affects between 50 to 93% or patients allergic to the pollen from birch trees.
[Skypala I. Fruits and Vegetables. In: Skypala I and Ventner C, eds. Food Hypersensitivity: Diagnosing and managing food allergies and intolerance. Oxford: Blackwell 2009: 153-156.]
What symptoms do they get?
Affected people often get lip tingling or redness and swelling of the lips and tongue and back of the throat. Some may experience itching or tightness of the throat. These symptoms only occur immediately after eating certain raw fruit and vegetables.
How does this happen?
The main allergen in birch pollen is something called Betv1 (a protein). Proteins are made up of a sequence of building blocks called amino acids and the sequence of the amino acids is very important in dictating which protein will be produced. Each sequence is different for each protein but different proteins can be similar in certain parts of the sequence. This particular Betv1 protein has an amino acid sequence which is extremely similar in parts to another group of plant proteins called PR10 proteins.
So what?
These PR10 proteins are found in fruit and vegetables such as apples, pears, cherries, stoned fruit, kiwi, celery, carrot and hazelnut (and there are more). So, a birch-pollen allergic individual who eats any of the above mentioned raw fruit or vegetables may well develop symptoms because the body mistakes the PR10 protein for the Betv1 birch pollen protein.
Why only raw fruit and vegetables?
The part of the Betv1 and PR10 protein that cross-reacts (and is the allergen) is not stable after heating. Therefore, cooking the fruit or vegetable breaks down the allergeneic protein, making it unable to be recognized by the body’s immune system and therefore not allowing it to cause an allergic reaction.
Why do affected people only get symptoms in and around the mouth?
Again the allergeneic protein is broken down by digestive enzymes in the gut so the symptoms stay localized to the mouth.
What can be done about it?
Current guidance is to avoid the food which causes symptoms or to eat cooked or canned variants of the food. Avoidance of all fruit and vegetables is not advocated, only the problematic foods, but if you are symptomatic to a whole range of fruit and vegetables, it would be best that you seek the help of an Allergy Consultant.
Regards,
Sandy
Dr Sandy Flann, Consultant Dermatologist
