What are cross-reactions?
When individuals with pollen allergy experience discomfort when eating raw fruit and vegetables, this is due to the fact that the proteins in these foods are so similar to the allergy-provoking substances in pollen that the immune system fails to see the difference. An allergic reaction thereby occurs, which we refer to as cross-reaction.
Who gets cross-reactions?
Individuals most affected by pollen allergy are also the 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 individuals react is highly individualised, and not all individuals 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 when 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 itching in the ears. The symptoms may increase and spread to other organs and in worst cases may result in anaphylactic shock, but this is very rare in Northern Europe.
Prevalence of cross-reactions:
Approximately 70 % of individuals with birch pollen allergy have a reaction to foods – most commonly nuts, kiwi fruit, raw carrots, apples and pears. Individuals with mugwort allergy may react to celery and several types of herbal seasoning. Generally, the pollen allergy develops first and the cross-reactions appear subsequently. Knowledge of the cause of cross-reactions is useful if one is to avoid symptoms.
Treatment of cross-reactions:
Drugs play a minor role in the preventive treatment of cross-reactions. Antihistamine preparations may be used, but the effects are uncertain. Immunotherapy in food allergy is not yet a practical possibility, but may be so in the future. Some studies suggest that immunotherapy in birch pollen allergy may have positive effects on the cross reactions.
In Norway, serious reactions as a result of cross-reacting foodstuffs occur only very rarely. The few individuals who do experience severe allergic reactions should carry an Epipen.
Investigation of food allergy in cross-reactions:
A thorough medical history is essential. Skin-prick tests with raw fruit and vegetables should be performed using the actual foodstuff using the prick-prick method. Specific IgE (blood test) may be useful, but rarely produces further information.
Table of cross-reactions
|
Birch (and often alder and hazel) |
Timotei and other grass species |
Mugwort |
|
Hazelnuts, walnuts, Brazil nuts, cashew nuts |
Grain varieties:
Barley, rye, wild oats, wheat |
Celery |
|
Stone fruits: apples, pears, peaches, cherries, nectarines, plums, apricots |
Pulses:
e.g. Soya beans |
Leeks |
|
Carrot (raw) |
Melon |
Capsicum |
|
Potato (raw) |
|
Onion |
|
Kiwi fruit |
|
Herbs/dried herbs, parsley, capsicum, coriander, garlic, cinnamon, aniseed, oregano |
|
Celery |
|
Sunflower seeds |
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 that individuals avoid the food or foodstuffs to which they suffer 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 Moon Daisy, Dandelion, Asters and Crysanthemums. 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 simple 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; individual species were tolerated. It may therefore be an idea to try various types. Red apples are often better tolerated than green. The apple may 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 sensitive than other people to shellfish (crustaceans, mussels, oysters and snails).
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 Useful facts on latex allergy).