A cross allergy is a form of allergic reaction. In an allergic reaction, certain antibodies ( IgE antibodies ) react to an allergen (for example pollen) and an allergic reaction occurs, for example in the form of rash or irritation of the mucous membranes with itchy eyes and increased sneezing. In a cross allergy, the antibody triggers an allergic reaction not only in contact with the source allergen (for example, the pollen) but also in contact with certain other allergens (for example, kiwis). It varies greatly from person to person whether and to what extent a cross-allergy exists and what other allergens it includes.


If the human body is confronted with an allergen, increased sensitivity may cause it to produce antibodies to this allergen. It then comes with every renewed exposure to the allergen to an allergic reaction. The antibodies recognize specific patterns on the surface of the allergen. If they bind to or couple to these leads to the triggering of an immune reaction that leads to the allergic reaction. The antibody recognizes the pollen on the surface of which it can dock, thus triggering an immunological reaction and the affected person notices that he has, for example, red, itchy eyes. In a cross allergy, the antibody also binds to patterns on the surface of allergens. However, they are not exactly the same as the original allergen, but they are very similar to it. This leads to the fact that even substances that originally did not trigger an allergic reaction actually do so.

Allergens and possible cross-allergens



Other pollen: beech, alder, oak, ash, hazel

Foods: nuts, carrots, tomatoes, soy, many pome and stone fruits, strawberry, parsley, pepper

pollen grains

Other pollen: ryegrass, cereals (such as wheat, spelled, barley, oats, millet, corn, rice)

Foods: cornmeal


Other pollen: ball grass, smoked grass, meadow willow grass

Cereals: oats, barley, rye, wheat

Foods: raw potatoes, legumes, kiwi, (water) melon, tomatoes, peas, peppermint, various herbs


Other pollen: birch, chamomile, dandelion, daisies, sunflower

Foods: peppers, celery, carrots, potatoes, cucumber, kiwi, apple, many common spices and herbs etc.


Other pollen: lilac, privet, olives




Foods: banana, melon, chamomile


Other nuts: cashew, hazelnut, almonds, poppy, pistachio, sesame, walnut

Foods: peanut, strawberry, kiwi


Other legumes: bean, peanut, lentils, soy, lupine


Pollen: mugwort, birch, grasses

Food: pineapple, apple, carrot, potato, rye and wheat flour, latex


Pollen: mugwort, birch

Food: Carrot, many common spices

cow's milk

Food: Beef and veal, soy, beef hair

House dust mites

Food: especially crustaceans such as, shrimp, lobster, crayfish, crab, shrimp, etc .; Oysters, snails


Pollen: mugwort, ragwort, meadowweedgrass

Foods: avocado, raw potatoes, paprika, celery, tomato, banana, kiwi, mango, peach etc.


Other antibiotics: cephalosporins


For the diagnosis, the anamnesis is very important. Here it is very helpful if the patient, for example, already a (nutrition) diary leads in which he enters, after eating any food or after contact with which substances it has come to an allergic reaction. Based on this, the attending physician can perform the allergy test.

There are different variants of the allergy test. Either on the patient himself or on his blood. The aim of the test is the controlled exposure of the patient to the possible allergen. After this exposure it is tested if an allergic reaction develops. Relatively well known is the so-called prick test in which the allergen to be tested is applied to the skin and introduced with a kind of small needle into the skin so that the respective substance can penetrate into the skin surface. It is then assessed whether reddening of the skin or swelling of the skin area develops. The prick test is performed mainly by dermatologists and special allergists.

Accompanying symptoms

Symptoms that can occur in the context of a cross-allergy are the same as in a normal allergic reaction. There are many possible manifestations. Redness, rashes and wheals may appear on the skin. The rash can be accompanied by itching. It can also cause a swelling of the nasal mucous membrane with cold and nasal congestion, the eyes may be red, tears and itchy. Often, allergies such as pollen allergy also cause symptoms such as frequent sneezing. Also, a narrowing of the airways in the sense of asthma can be triggered by an allergic reaction. In the gastrointestinal tract, contact with an allergen may cause diarrhea, nausea and abdominal pain. An allergic reaction can be harmless but also life threatening.

  • Rash due to pollen
  • Blushed eyes - The different causes
  • Hoarseness due to an allergy

Treatment / therapy

Cross-allergies often affect different types of foods. If such a cross-allergy to a food, so it is usually sufficient to avoid this food. Many foods also help to warm them as they lose their allergenic character. An example of this is carrots or potatoes. In their raw state, they have a high allergenic potential, but barely when cooked. Often, however, it is not safe to identify all the substances to which the person is allergic. Then it can be helpful to take medicines that have an anti-allergic effect, thus counteract the symptoms that an allergy brings with it. A disadvantage of these drugs is that many patients complain that they are very tired. However, there are different agents that are different from each other.

In cross-reactions occurring as part of a pollen allergy, sufferers often report that the symptoms of eating the affected foods are pronounced only during the pollen season and significantly decrease in autumn and winter so that it is sometimes sufficient to avoid these foods during the pollen season. For some substances, hyposensitization may also be considered as a treatment option. The goal here is to get the body used to the allergen over a longer period of time. This is done by regularly exposing the allergen to low doses. If a hyposensitization is successful, the body will no longer respond with an allergy to the substance in question. Hyposensitization is not always successful and relatively time consuming.

  • Medicines for hay fever
  • Food allergy


As described above, there are cross-allergies that are season-dependent and occur, for example, especially in spring and autumn. For all other cross-allergic forms, however, once sensitization has taken place, the allergy usually persists. Its degree of manifestation may change, but it rarely disappears completely. Therapeutically, a hyposensitization can be used to achieve (almost) complete disappearance of the allergic reaction to a particular allergen. However, it can not be applied to all allergens.



An allergy to grass pollen is one of the most common allergies and is commonly referred to as hay fever. There are numerous cross-allergies that can be associated with an allergy to grass pollen. Foods that can be allergy include potatoes, peas, kiwis, tomatoes, peanuts, soy and melon. On cereals such as rye, wheat, oats and barley allergies can develop, this can significantly complicate the diet.

Birch / alder

If there is an allergy to birch pollen, cross-allergies can also be present with pollen from many other plants such as alder, ash, oak and beech. Various foods may also be the target of birch pollen cross-allergy. These include nuts such as hazelnuts and walnuts, almonds, carrots, milk and soy milk. Many fruit products can also be affected by a cross reaction. These include apples, pears, peaches, nectarines, cherries, berries such as raspberries or strawberries and blackberries and plums. In rarer cases kiwis as well as vegetables like celery or tomatoes can be affected. Numerous herbs and spices can also lead to a cross allergy, including parsley and pepper.


If there is an allergy to apples this is in most cases not a direct apple allergy but a cross allergy. The main allergens in this case are often pollen of different trees, for example birch pollen. Research has shown that not all apple varieties have the same allergenic potential. In particular, the more well-known apple varieties offered in the supermarket such as Braeburn, Golden Delicious and Granny Smith should be able to trigger cross-allergies while the more unknown older apple varieties such as Boskoop which are offered in particular at weekly markets are less likely to trigger allergies. Also, the preparation of the apples is crucial for an allergy. Thus, an allergic reaction, especially in raw and unprocessed consumed apples whereas apple sauce or apple pie often makes no problems. Even grated apple should be better tolerated than not processed apple.

Penicillin / amoxicillin

Allergies to antibiotics such as penicillin occur relatively frequently. However, there are other antibiotics besides penicillin which belong to the group of penicillins. These include, for example, amoxicillin and flucloxacillin. Patients with allergy to penicillin are also relatively likely to be allergic to these substances. Another group of antibiotics is a cross-allergy due to a molecular building block, a beta-lactam ring, which is found in both antibiotic groups. This group are the cephalosporins. These include cefuroxime, ceftriaxone and ceftazidime. Even with antibiotics from the group of carbapenems can theoretically occur a cross allergy as these also contain a beta-lactam ring. If there is an allergy to an antibiotic, this is manifested, for example, by a rapid onset of rash shortly after ingestion. The skin may turn red, pustules or wheals may develop. There is a risk of edema (swelling) in the area of ​​the larynx, which can be life-threatening. An allergy to antibiotics occurs only when sensitization has already taken place. This means that in the first patient taking a drug from the group of penicillins, cephalosporins or carbapenems usually no allergic reaction can develop. However, this can already occur with the second medication. There are also reactions to antibiotics that show up only after a few days to weeks.

  • Rash after antibiotics
  • Allergy to amoxicillin
  • Rash due to amoxicillin

latex allergy

If there is a latex allergy, cross-allergies can be found on many foods. The most well-known cross allergy in a latex allergy is on bananas.
But also on

  • passion fruit
  • mango
  • papaya
  • kiwi
  • peach
    such as
  • tomato
  • celery
  • Paprika,
    such as
  • chestnuts

can show an allergic reaction.

Rye / wheat

An allergic reaction to rye and / or wheat usually develops as part of a cross-reaction. The primary allergen are mostly grain pollen. Allergy to grain pollen can also lead to cross-allergies to potatoes, peas, kiwi, melon, tomatoes and other grains such as oats and barley. It should be noted that such allergies usually occur only in food in its raw form, boiled or similarly prepared potatoes thus trigger usually no allergic reaction and can thus be safely consumed.

Peanut / hazelnut

If there is an allergy to nuts then the nut may be the primary allergen or a cross allergy. If it is a cross allergy so come as a primary antigen, for example, birch pollen or grass pollen in question. A nut allergy can also exist as such, the nut is then the primary allergen. Again, other foods can become cross-allergens. These include almonds, poppy seeds, sesame, pistachios, kiwis and strawberries. Peanuts are not among the actual nuts (nuts) but to the legumes, but they could also act as a cross-allergen in an allergy to grass pollen.

Walnut and almond

Cross allergies with walnuts and almonds play a role especially in people with a birch pollen allergy. A particular allergen of the birch, the so-called major allergen, resembles proteins that are also present in walnuts and almonds. The immune system can not sufficiently differentiate this similarity and thus responds to both with an allergic reaction. The food allergy is rather mild. The protein, which triggers the allergic reaction in walnut and almond, is destroyed by heat and becomes digestible for allergy sufferers.

In addition to walnut and almond, there is also a cross allergy to birch pollen in many other fruit and vegetables. In addition, other nut allergies may also be cross-allergic to both almonds and walnuts. Here the patients react to another protein in the nuts. This is not sensitive to heat in contrast to the one described above. For this reason, care must also be taken to ensure that nuts are included in processed products. The allergic reaction is rather strong, no matter which nut is consumed.


An allergy to kiwi can occur in the context of a cross-allergy. Possible primary allergens include nuts, birch pollen and grass pollen. But a kiwi allergy can also exist without cross allergy. Allergies to grass pollen, latex and foods such as pineapple, apples, carrots, potatoes, and rye and wheat flour can all cause cross-allergies.


An allergy to citrus fruits is rather rare. Cross allergies are not known yet. If there is an allergy to mandarins their consumption should be avoided.


An allergy to tomatoes can exist in the sense of a cross allergy. The primary allergen is then usually birch or grass pollen. In people who are allergic to pollen, the symptoms usually disappear in autumn and winter, often in these months, the cross-allergies are barely noticeable, for example, tomatoes can be better consumed in the autumn and winter months. Whether this is actually the case, of course, every person affected must try out for themselves individually.


A cross-allergy to strawberries can develop in people with birch pollen allergy or nut allergy.

Mugwort (pollen)

Food: Vegetables such as paprika, celery, carrots, tomatoes, potatoes and cucumber; Fruits like melons, mangoes, apples and peanuts

Pollen: birch, dandelion, sunflower

Numerous spices and herbs such as coriander, chili, dill, ginger, chamomile, garlic, cumin, nutmeg, pepper, cinnamon, parsley, thyme, basil


In a mugwort allergy is also a cross allergy to peppers known. In addition, the birch pollen allergy is a cross allergy to paprika, which is often used as a spice. A third cross allergy to peppers is known for a latex allergy. Certain proteins in latex are similar to those of peppers and many other fruits and vegetables, which is why it comes to the cross-reaction.


Especially spices like anise, basil, dill, fennel, oregano, cumin, coriander and thyme

cow's milk


cat hair

With allergy to cat hair, there is no such marked cross-reactivity as is the case with pollen or grasses. A well-known cross-allergy is pork. However, this is not very pronounced and the risk that it actually comes to a reaction when eating pork, is very low.


Cross allergies to nickel are known from the dental field. There are cross allergies for example to palladium or cobalt. Rarely do people with a nickel allergy also react to copper or chromium.

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