You may be allergic to fruit

Food allergy

If the immune system reacts allergic to a certain substance in the food, one speaks of food allergy. A real food allergy is rare, only 1–2% of the population suffer from it. Most of the time the symptoms are mild to moderate; rarely, they can be life-threatening.

Short version:

  • Food allergies are very rare and differ from food intolerance.
  • The most common allergies in children are milk, eggs and nuts. Adults are mostly allergic to nuts, fruits, and shellfish.
  • Most of the time the symptoms are mild to moderate; rarely, they can be life-threatening.
  • Anaphylactic shock is a case for the emergency doctor.

How does a food allergy develop?

Allergies are diseases that take place in the body's defense system (immune system). In order to protect the body, the immune system tries to recognize and fight off various foreign substances. Hypersensitive people also react to substances that others tolerate without reaction and actually pose no threat to our body. You develop an allergy.

In the case of a food allergy, the immune system recognizes certain food components as foreign and dangerous and sets a defense process in motion. Through the mediation of different cells, unusually large amounts of defense substances (antibodies of the IgE type) are formed. They attach to certain cells and cause them to release histamine and other tissue hormones.

Histamine is responsible for many of the body's reactions to allergies. For example: reddening of the skin, swelling, narrowing of the windpipe, increased permeability for fluid from the blood vessels. This leads to violent reactions, especially on the mucous membranes of the intestines, eyes, nose and bronchi and on the skin. For example: diarrhea, watery eyes, runny nose, asthma attack with shortness of breath, rash, reddening and itching of the skin.

Upon first contact with the allergy-causing food, the immune system recognizes a protein (incorrectly) as dangerous and begins to produce antibodies of the IgE class. With every further contact with the substance, the immune system recognizes this substance and will fight it off quickly and intensively. This leads to an allergic reaction.

Examples of allergy-causing foods and triggers that merge into one another (cross allergies)

  • In principle, all foods can cause an allergic reaction. The most common in children are allergies to milk, eggs, soybeans, wheat. As already mentioned, these types of allergies heal with age.
  • Adults mostly suffer from pollen-associated food allergies, e.g. to nuts, fruits and vegetables or spices.
  • Food allergies to peanuts, fish and seafood are rare and dangerous forms of allergy.
  • Birch pollen reacts crosswise with types of nuts, apples, pears, cherries, walnuts, almonds, plums, kiwi, potato peel, tomatoes and carrots. This means that an allergy to birch pollen can also cause allergic reactions to the mentioned fruits and vegetables. These types of allergies are usually uncomfortable, but not dangerous.
  • Mugwort pollen reacts crossed with celery, spices and carrots. These forms of allergy can also cause severe allergic reactions up to anaphylactic shock.

What are the symptoms of a food allergy?

  • A tingling sensation in the oral cavity and on the lips
  • Puffy lips and face
  • Vomiting, stomach cramps, diarrhea
  • Suddenly runny nose
  • Swelling of the larynx, asthma, shortness of breath
  • Itchy skin, rash, swelling
  • Drop in blood pressure
  • A shock reaction (anaphylactic shock) occurs very rarely. This can lead to a circulatory collapse and must therefore be treated immediately by an emergency doctor.

Food intolerance usually manifests itself in digestive problems. They differ fundamentally in their development from food allergies: While allergies are triggered by an excessive reaction of the immune system, intolerance is the inability of the intestinal mucous membrane to absorb or utilize certain substances from food. However, the immune system is not involved in this process.

Food allergies are very common in people who are allergic to pollen. In the case of these so-called "cross allergies", not only do pollen trigger allergic reactions, but also foods that happen to have a similar protein structure and are therefore mistaken for the immune system. The symptoms are usually mild. Allergens from different plant and animal species, which supposedly have nothing in common, can nevertheless have a similar allergy-causing protein structure. Most often, cross allergies develop from an allergy to early bloomers such as birch, alder or hazel. Those affected then often react to nuts, pome and stone fruits, celery or carrots with itching or scratching the throat. Allergy sufferers who have dust mite problems often react to other types of mites; very rarely a cross-reaction is to be expected when eating shellfish.

How can a food allergy be avoided?

  • If you are allergic to certain substances, you should avoid them and watch out for parallel or merging reactions.
  • Get advice from an allergist.
  • Pay attention to the first signs of allergy; if you are worried, call a doctor.

How does the doctor make a diagnosis?

  • The doctor will draw up a medical history and isolate the substances that are causing the allergic reaction in your case.
  • It excludes other diseases that cause similar symptoms, such as celiac disease (gluten intolerance), food intolerance, minor poisoning, nervous bowel or chronic bowel disease (ulcerative colitis and Crohn's disease).
  • With a skin test on the forearm or on the back (prick test).
  • The concentration of antibodies against a specific antigen can be measured in the blood (radio-allergen-sorbent test).
  • The exclusion and provocation diets are suitable for excluding an allergy: the patient must adhere to a low-allergen water-rice-potato diet for seven days. If he is not symptom-free afterwards, a food allergy is unlikely. A skin test is carried out beforehand to rule out a potato or rice allergy. If there is no symptoms, individual foods are now gradually added until symptoms arise. This is how you identify the corresponding food.

Possible complications

The mucous membranes in the mouth and throat can swell and cause shortness of breath. An asthma attack and / or anaphylactic shock can occur.

How are food allergies treated?

Of course, you should not eat the allergy-causing food if possible.

The disease cannot be cured medically, but there are various means that can alleviate the symptoms:

  • Antihistamines
  • Mast cell stabilizers prevent the release of histamine.
  • If shock reactions have occurred before, it makes sense to carry a shock pharmacy with antihistamine, cortisone and an adrenaline self-injection device.

+++ More on the topic: Food intolerance +++

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Prof. Dr. Christof Ebner (first author 2013), Silke Brenner (2019)
Medical review:
Prof. Dr. Gunter Sturm
Editorial editing:
Dr. med. Stefanie Sperlich, Mag. Julia Wild

Status of medical information:

AWMF guidelines for the management of IgE-mediated food allergies, Reg. 061-031, valid until February 26th, 2021 at (last accessed: July 3rd, 2019)

Austria's public health portal: food allergies at (last accessed: July 3, 2019)

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ICD-10: K52.2, L27.2, T78.0