Our Blog post this edition comes from Jemma at Allergy Resources.
Jemma writes content for the Allergy Resources website at www.allergyresources.co.uk
, compiling lots of resources for the more unusual food allergies as well as the Top 14. She is interested in the cross reactivity of allergenic proteins and allergic syndromes and makes a monthly compilation of all the most interesting allergy, asthma and eczema news from around the world.
She regularly shares allergy content on Twitter
Fruit allergies are relatively common, but there is a lot less information about them as they are not easily defined and categorised. Here we aim to provide more information on the different allergenic proteins which may be the cause of allergic reactions to fruits.
We are defining fruit as “… the product of a tree or plant which contains seeds and can be eaten. These are generally sweet and fleshy.”
Fruit allergies can generally be split into three categories.
1 – Fruits causing mild
“Oral Allergy type” symptoms
2 – Fruits with seeds causing severe
allergy symptoms due to cross reactivity
3 – Fruits which contain other panallergens and can cause allergic symptoms from mild to severe
1 – Pollen Food Allergy Syndrome
Fruit allergies are commonly linked to Pollen Food Allergy Syndrome, which was previously called Oral Allergy Syndrome. These terms are still used interchangeably.
In this syndrome a person first becomes sensitised (allergic) to a tree or plant pollen. The most common in Pollen Food Allergy Syndrome is birch tree pollen. The allergenic protein in birch tree pollen is called Bet v 1
. A person can then find themselves allergic to other proteins in foods which are similar to Bet v 1 proteins, often called Bet v 1-like or Bet v 1 homologues. Bet v 1 proteins are found in a wide range of foods including fruits, vegetables, nuts, seeds and grains.
The symptoms of this syndrome are called oral allergy symptoms as they can cause sneezing, itchy mouth and lips as well as a scratchy throat and tongue. All in all, these fruits can cause a general irritation of the mouth, nose and throat. It is very rarely serious enough for the throat to close as it does in anaphylaxis.
The Bet v 1 allergens are often referred to as ‘heat labile’, meaning that the proteins are damaged by heat and lose their ability to cause an allergic reaction. There are more proteins in the skin of the fruit than in the flesh and seeds. If you can eat the fruit once heated or peeled with no or reduced allergic reactions then you should be able to determine if this is Pollen Food Allergy Syndrome or a true IgE allergy (an IgE allergy will have immediate symptoms which may include anaphylaxis, swelling and/or hives).
Fruits containing Bet v 1 allergens are cherry, apple, peach and pear.
2 – Seed Allergies
There have been an increasing number of studies on fruits with small hard seeds which contain seed storage proteins
. Seed storage proteins are more commonly associated with nut, seed and legume allergies and have a greater potential to cause a severe allergic reaction which may include anaphylaxis if these seeds are accidentally ingested.
Seed storage proteins are heat stable, meaning that heating (and in many cases, freezing or processing) does not damage the shape of the protein, so it does not lose its ability to cause allergic reactions.
Fruits shown to contain seed storage proteins are lemons, kiwi and coconut.
3 – Other Panallergens
Panallergens are allergenic proteins which can cause more severe allergic reactions over lots of groups of foods and cause people to suffer from multiple food allergies. The most studied are Bet v 1 and seed storage proteins (covered above), but profilins, hevein and lipid transfer proteins also play a big part in allergic reactions to fruit.
Allergic reactions to these panallergens are likely to be more severe than oral allergy symptoms, but less likely to be anaphylactic like seed storage reactions.
are found in a variety of fruits, vegetables, seeds and grains as well as plant and tree pollens. Fruits containing profilins are apple, cherry, orange and peach.
is the allergenic protein responsible for Latex Allergy, it has cross reactivity with similarly shaped proteins in the skin of the fruit which can cause an allergic reaction; this is called Latex Food Syndrome. Hevein allergy is usually linked to the skin of fruits such as banana, mango, jackfruit and kiwi.
Lipid Transfer Proteins
(also called LTPs) are panallergens found in many groups of foods and can cause serious allergic reactions. It is often the allergen found to be linking what initially looks like lots of random food allergies together. Fruits containing LTPs are apple, banana, cherry and peach.