Hazelnuts are the edible nuts of the hazel tree which is in the Betulaceae family of plants. Other trees in this family of plants include alder, birch and hornbeam.

There are 8 allergens associated with an allergy to hazelnuts. There are 3 additional allergens that are associated with hazel pollen.

Cor a 1 is an airway allergen and is a Bet v 1 protein. These proteins are associated with pollen, but can sometimes give oral allergy symptoms after eating certain nuts, fruits or vegetables.

Cor a 2 is a profilin protein, these are panallergens which can cause allergic reactions across multiple foods.

Cor a 8 is a Lipid Transfer Protein (LTP). This group of proteins commonly causes severe allergic symptoms.

Cor a 9 is an 11S protein (also known as legumin like). Cor a 11 is a 7S protein (also known as vicilin like) and Cor a 14 is a 2S protein. These groups of proteins are involved in seed storage and are commonly found in many nuts, legumes and seeds. This is why a person suffering from a tree nut allergy is often allergic to whole groups of nuts, legumes and seeds.

Cor a 12, 13 and 14 are all oleosin proteins, these are proteins mostly associated with nuts and seeds. The proteins are involved in preventing the build up of oil molecules and may have role in lipid store degredation during plant germination.

Hazelnuts contain a moderate amount of lectins, another cause of food intolerance. Cooking foods with lectins makes them more digestible and can reduce the symptoms of food intolerance.

Hazelnuts are a food low in salicylates, so are unlikely to be a cause of gastrointestinal food intolerance symptoms in people who are sensitive to salicylates.

You can read more about Food Intolerances on the dedicated Food Intolerance Page.

Hazelnut allergy is often linked to LTP Syndrome, where similarly shaped proteins in other plants resemble those in hazelnuts and elicit an allergic reaction.

The Bet v 1 proteins are associated with Pollen Food Allergy Syndrome. If you are allergic to 3 or more foods in the cross reactivity section with oral allergy type syndromes then you may have pollen food allergy syndrome.

Allergy to hazelnuts is sometimes linked to Celery-Mugwort-Spice Syndrome as the sensitising allergen is a profilin protein called Art v 4, these proteins are also sometimes also called Bet v 2 proteins.

There is a link between hazelnuts and Latex Food Syndrome. The plant involved in latex allergy Hevea brasiliensis, the rubber tree plant, has an allergen called Hev b 8 which is a profilin protein. Those very sensitised to latex may have a contact allergic reaction from other foods or plants containing profilin proteins, there is less evidence of this than sensitisation to other latex linked proteins like hevein and chitinases.

Common foods involved in LTP allergy include kiwi, strawberries, sunflower seeds, walnut, apple, mulberry, banana, pea, apricot, cherry, plum, almond, peach pomegranate, raspberry, tomato, grape, celery, peanut, asparagus, cabbage, broccoli, chestnut, lemon, tangerine, orange, hazelnut, lettuce, lentils, lupin, green bean, pear, mustard, wheat and maize.

If sensitised to birch pollen you may have Pollen Food Allergy Syndrome and may also react to kiwi, pear, peach, plum, nectarine, apricots, cherries, tomato, celery, crrot, potato, parsnip, pepper, dill, cumin, peas, coriander, fennel, mung beans, walnut, almonds, peanuts, lentils and apples.

Hazelnut is broadly linked to other fruit profilin allergies. Allergy to celery, peanut, soyabeans, walnut, lupin, almonds, mustard, lychee, kiwi, pineapple, chilli, melon, orange, strawberry, apple, banana, aubergine (eggplant), peach, pear, tomato, dates, cherry, carrot, barley and wheat. Allergic reactions to some of these foods may be considered a marker of profilin hypersensitivity.

Other food containing 2S albumin seed storage proteins are cashews, peanuts, almonds, mustard seed, rapeseed, turnip, chickpeas, brazil nuts, pistachio, buckwheat, soya beans, sunflower seeds, walnuts, kiwi, castor beans and sesame seeds.

There is a lot of cross reactivity between 2S and 11S seed storage proteins, the only other food containing 11S proteins not mentioned above is pumpkin.

Other foods containing 7S seed storage proteins not mentioned in the list above are lupin, lentils, macadamia, peas and mung bean.

Oleosin proteins are also found in buckwheat, palm oil, sesame and peanuts.

You can download a Tree Nut Allergy Factsheet from the Allergy Resources Ko-fi Shop for just $0.90 (£0.69 or €0.82). This has up to date information on which foods contain linked allergens and what foods to avoid if you think you have an allergy to tree nuts.

Please note that these food lists are not exhaustive, the most up to date in information is on the Cross Reactivity Tool.

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