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Allergies are caused by reactions of the body’s immune system to a wide variety of sources. These include animal products, mites, moulds, latex, pollen, medicines, plants, venom as well as food. Most of the non-food related allergies can be accompanied by reactions in the mouth or the gastrointestinal tract. The proportion of individuals experiencing these gut reactions to non-food allergies varies widely depending on the allergy and also the population. Up to 80% of individuals with certain pollen allergies, for example, have reactions involving the mouth or intestinal tract.

The reason for the cross-reactions lies in the structural similarities among proteins of diverse sources, such as pollens and foods. Current molecular research is providing helpful information in the prediction of cross-reactions .

Frequency in population

  • Approximately 70% of individuals with food allergies also have other allergies, including hay fever.
  • Hay fever (allergic rhinitis) occurs in 15-20% of the population and about 50% of these will have some form of mouth (oral allergy syndrome; food contact hypersensitivity) or, less frequently, intestinal allergic reaction.
  • Birch pollen allergy is the form of hay fever most commonly accompanied by food allergies in the Western developed world – in up to 80%.
  • Between 30-80% of individuals with latex allergy have associated allergic reactions to food.
  • Cross-reactivity between shellfish and house mite allergy is quite common.
  • Children with atopic dermatitis / eczema have a high prevalence (at least 30%) of food allergies, predominantly cow’s milk, egg and peanut.
  • The incidence of food-induced asthma in children is about 6% (rarer in adults), with the most frequent offending food allergies being milk, eggs, and peanuts.

Individual types of allergy

Allergies often involve multiple organs, e.g. gastrointestinal and respiratory systems including the sinuses, the eyes, skin and even the nervous system. Careful observation and history taking by the physician are essential to discover patterns of associations between allergies.
Common cross-reactions between pollen and food

  • Birch pollen: apple, carrot, celery, pear, tomato, cherry, tree nuts (infrequently: many more fruit and spices)
  • Goosefoot pollen: banana, melon, peach (infrequently: nectarine, asparagus, kiwi, potato, olive, onion)
  • Mugwort pollen (weed): carrot, celery, aniseed, peach (infrequently: many more fruit, vegetables and spices)
  • Ragweed pollen: melon, cucumber, banana, sunflower
  • Timothy grass: apple, litchi, tomato, celery, corn, bell pepper, paprika

Most individuals with hay fever cross-react with two or more foods. The most frequent symptoms are tingling, swelling, itching in the mouth or on the lips, but about 10% have intestinal symptoms.

Common cross-reactions between different foods

  • Shrimp, lobster, crab, less common: squid, scallops, clams, oysters (associated: mite allergy)
  • Squid, scallops, clams, oysters, less common: shrimp, lobster, crab
  • Peanut, lupine
  • Tree nut (walnut, hazelnut, Brazil nut, pecan), pistachio, cashew
  • Cow’s milk, all mammal’s milk (e.g. >90% with goat and sheep milk, beef meat (10%!))
  • Hen’s egg, rarely other bird’s eggs and poultry meat
  • Cereal (wheat, oat, barley, rye, millet, sorghum, maize, rice): cross-allergy not common. 20% cross-react with one other cereal.
  • Flour allergy – consider mite contamination.
  • Fish, frequent cross-reactions, even between salt and fresh water fish. Not to shellfish. Distinguish from histamine intolerance (i.e. non-allergic, see Biogenic amines)
  •  Seeds, sesame, mustard, sunflower
  • Peach and melon commonly cross-react with other fruit (generally mild reactions)

Latex- fruit allergy syndrome –latex contact allergy associated with food allergy in 30-80% of cases

  • Latex, bananas, avocado, chestnut, apple, kiwi, potato, tomato, melon, papaya. Less common: fig, pineapple, peach, pear, passion fruit, walnut, hazelnut, almond, grapefruit, strawberry, spinach, lettuce, celery, diverse spices. Contact allergy with latex products, as well as certain plants (e.g. fig, gum, oleander, cactus).


Allergic reactions involving the alimentary tract can result in a wide range of symptoms, stretching from harmless tingling of the mouth to life-threatening shock reactions and from lasting a few hours to many days. At least 30% of sufferers will have symptoms resembling functional bowel disorders, such as irritable bowel syndrome, functional diarrhea or functional dyspepsia: nausea, vomiting, bloating, abdominal cramps and pain, diarrhea, swallowing problems or reflux. Tingling, swelling, itching of the mouth, tongue and throat are frequent allergic signs relating to the pollen-associated oral allergy syndrome (food contact hypersensitivity syndrome), which is the commonest food allergy in teenagers and adults. These symptoms often increase in parallel with hay fever. Other possible manifestations of food allergies are skin reactions, such as itching (urticaria), rash, edema or swelling, and respiratory problems, such as runny nose, sinusitis, asthma or bronchitis. Nervous system reactions, such as tiredness, chronic fatigue, loss of ability to concentrate, migraine headaches and psychiatric disturbances, and musculoskeletal symptoms, including joint and muscle pain, are increasingly recognized. Food allergy may result in reactions outside of the intestinal tract, such as eczema, devoid of any intestinal symptoms. At the extreme end of the spectrum anaphylactic shock can ensue.

Atopic dermatitis/eczema is associated with egg, cow’s milk and peanut allergy and removal of the allergens results in significant improvement in most children. Most cases improve by teenage years, but some develop respiratory allergy.


The most important aspect of allergy management is accurate recognition of the offending food(s) or other agent(s) (See Food allergy tests). Permanent exclusion of even small amounts of the recognized component(s) from the diet is currently considered to be of prime importance, as this prevents the occurrence and escalation of symptoms. A total elimination diet is often difficult, depending on the food component(s), frequently requiring expert dietary advice and a great deal of personal motivation and discipline. Careful reading of food, drug and in some cases household and cosmetic product labels is advised. Advice on food substitution is crucial in the case of fruit or vegetable allergies to prevent deficiencies.

The allergenic potential of many components is reduced, but generally not eliminated, by cooking and processing, with the exception of peanut and tree nut.

If complete elimination is not achieved or achievable, there is some evidence certain types of anti-allergic medication may be helpful. These include cromoglycate, ketotifen, a combination of antihistamines and probiotics. There is currently insufficient evidence to support the use of steroids or more novel agents, except in the case of eosinophilic intestinal disease. Emergency treatment injectors (e.g. Epipen™) should be carried in case of severe allergic reactions. Immunotherapy (desensitization) for some allergies, especially the pollen-associated food allergies, may be successful in a subset of individuals, however even then the effect is often not long-term. Other treatments in development include vaccination, anti IgE and other antibodies, toleragen peptides, recombinant epitopes for hyposensitization, anti-mast cell drugs, as well as molecular modification of the offending food protein.

Information nuggets

  • Food allergy cross-reactions with pollen may increase during pollen season and decrease subsequently. Therefore, certain foods may be tolerated only outside of the high pollen season.
  • If fish allergy exists, it is best to avoid all fish due to high cross-reactivity.
  • Reactions to fish, especially if not fresh, may involve histamine sensitivity rather than allergies (See Biogenic amines).
  • The most common fruit allergy cross-reactions are with peach and melon.
  • Food allergy may cause symptoms outside of the intestinal tract, such as eczema, without inducing relevant intestinal symptoms.

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