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Useful facts on cross-reactions (kryssreaksjoner)

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Useful information concerning cross-reactions – NAAF’s fact sheet

What are cross-reactions?

When individuals with pollen allergy experience discomfort when eating raw fruit and vegetables, this is due to the fact that their immune system fails to “see” the difference between the allergy-provoking substances in pollen (proteins) and protein in the foods. An allergic reaction thereby occurs when the person allergic to pollen eats these foodstuffs. This applies in particular to those allergic to birch pollen.

Who experiences cross-reactions?

Individuals most affected by pollen allergy are also those most vulnerable to cross-reactions. Some individuals with pollen allergy only suffer food reactions during the pollen season, whilst others may have symptoms throughout the year. How a person reacts is highly individualised, and not all those allergic to pollen suffer cross-reactions.

What symptoms can cross-reactions cause?

Many individuals allergic to birch pollen will experience discomfort in the mouth and throat after eating raw fruit and vegetables, particularly during the pollen season. The term “oral allergy syndrome” is used in food hypersensitivity, where local symptoms from the oral cavity dominate. Some individuals may experience tingling/itching as far as in the ears. The symptoms can increase and spread to other organs and in extreme cases may lead to anaphylactic shock, but this is very rare here in Northern Europe.

Incidence of cross-reactions:

Approximately 70 % of individuals with birch pollen allergy have a reaction to foods – most frequently nuts, kiwi fruit, raw carrots, apples and pears. Individuals with mugwort allergy may react to celery and many types of herbal seasoning. Generally, the pollen allergy develops first and the cross-reactions appear later. Knowledge of the cause of cross-reactions is useful in order to avoid symptoms.

Treatment of cross-reactions:

Medicines play a minor role in the preventive treatment of cross-reactions. Antihistamine preparations may be used; however, their effect is uncertain. Immunotherapy in food allergy is not yet a practical possibility, but may be so in the future. Some studies suggest that immunotherapy with birch pollen allergy may have positive effects on the cross reactions.

Investigation of food allergy in cross-reactions:

A thorough medical history is the most important factor. Skin-prick tests with raw fruit and vegetables should be carried out using the foodstuff itself, using the prick-prick method. A specific IgE (blood test) may be useful, but seldom produces further information.

Common cross-reactions, pollen allergy

Birch, hazel, alder, Salix (osage orange, goat willow, willow)

Timothy-grass (timotei) and other grass varieties


Apples (raw

Pears (raw)

Pulses (beans, peas, lentils)


Stone fruits (peaches, nectarines, cherries, morello, plums, apricots, almonds, mango)

Wheat, barley, rye, oats

Leeks, onions, garlic

Carrot (raw)

Potato (raw)


Herbs/dried herbs and herbal medicines (parsley, basil, oregano, coriander etc.)

Hazelnuts, Brazil nuts, walnuts






Sunflower seeds






  • If a person has mite allergy, cross reactions occasionally occur with shellfish and molluscs
  • If a person has latex allergy, cross reactions can occur with kiwi, avocado and banana
  • If a person has grass pollen allergy, allergy tests often have a positive indication for wheat and legumes; however, this is rarely associated with allergy symptoms.


Good advice for cross-reactions:

When cross-reactions to a foodstuff occur, the individual does not necessarily react to the other foodstuffs in the cross-allergy list. Food is most often tolerated boiled, peeled, canned or preserved. It is recommended to avoid the food or foodstuffs that cause a reaction. Cross-allergy does not actually exacerbate the pollen allergy. There is no reason to believe that individuals with birch pollen allergy should avoid fruit and vegetables as a precautionary measure.

Mugwort belongs to the composite family, and an individual with mugwort allergy may react to other species in this family, such as oxeye daisy, dandelion, asters and chrysanthemums. An individual with mugwort allergy - with hypersensitivity to celery - will not normally tolerate either fresh or boiled celery, in contrast to individuals with birch pollen allergy who often tolerate boiled celery.

Fruit allergy in individuals with birch pollen allergy represents a minor problem for most, but may be problematic for some. They will often tolerate melon, pineapple, grapes, banana and citrus fruits. As a rule, they will also be able to eat raspberries, redcurrants, blueberries and lingonberries. German studies reveal that with provocation involving various species of apple, certain varieties were tolerated. It may therefore be an idea to try various types. Red apples are often better tolerated than green. The apple can also be peeled and left to stand for a while to reduce the degree of allergy.

Other types of cross-reactions:

People with allergy to mites or insects such as mosquitoes, mosquito larvae and cockroaches are often, more than other people, hypersensitive to shellfish (crustaceans, mussels, oysters and snails).

In those allergic to cats, an increased tendency towards allergy to bacon has been reported. Some individuals with latex allergy may develop allergic symptoms from exotic fruit and vegetables. Banana, avocado and kiwi fruit provoke the most frequent symptoms; cross-reactions may also be triggered by papaya, figs, potatoes, tomatoes and chestnuts (see separate fact sheet on latex allergy).

Fact sheet on cross-reactions has been drawn up in consultation with NAAF’s medical board.