Brief overview
- Description: Hypersensitivity of the immune system to actually harmless components of certain food. Usually these allergy triggers (allergens) are proteins, for example from nuts, cow’s milk or wheat.
- Symptoms: Itching, hives, swelling of the mucous membranes around the lips, mouth and throat, swollen, watery eyes, runny nose, vomiting, flatulence, diarrhea, abdominal cramps. In extreme cases, anaphylactic shock develops (danger to life!).
- Causes and risk factors: Genetic predisposition to allergy (atopy) in combination with favoring factors (such as smoking during pregnancy).
- Diagnosis: Medical history, allergy tests such as skin test, antibody determination, provocation test, omission diet if necessary.
- Treatment: Avoid allergy triggers. In acute cases, medication for more severe symptoms. If necessary, hyposensitization in case of peanut allergy or pollen-associated food allergy.
- Prognosis: Food allergy in young children often “grows out”. Allergies that occur later usually persist throughout life.
Food allergy: Description
In allergies, the immune system usually reacts to harmless foreign proteins – such as those from pollen (in hay fever) or dust mites (in house dust allergy) – and fights them. This is usually done with the help of antibodies of the type IgE (immunoglobulin E). In the case of a food allergy, the body’s defenses usually mistakenly classify various food proteins as a threat. However, this happens comparatively rarely: The number of people affected in the population is in the single-digit percentage range. Most of them are small children.
Certain foods (food groups) trigger food allergies more frequently than others. These include:
- Nuts (e.g. peanuts)
- Wheat
- Cow’s milk
- Chicken eggs
- Fish
- Soy
- Celery
Food allergy in children
Young children develop food allergies particularly easily because their intestinal wall does not yet function as reliably as that of an adult. Therefore, food components and cells of the immune system are more likely to come into contact with each other. As a result, the immune system can develop a hypersensitivity to certain food components and act vehemently against them.
Food allergy in children and adolescents is most commonly to cow’s milk, chicken eggs, soy, wheat, peanuts, and tree nuts (e.g., hazelnuts or walnuts).
Cross-allergies
Food allergies are often mediated by specific antibodies (immunoglobulin E) (type I allergies). These are directed against the food component in question. Sometimes, however, the antibodies are subsequently directed against allergens with a similar structure from other sources. Physicians then speak of a cross-allergy.
Thus, a food allergy in adults is usually such a cross-allergy, arising as a result of a pre-existing inhalant allergy. This is an allergy caused by inhaled allergens (e.g. pollen allergy = hay fever).
For example, people with an allergy to tree pollen (such as birch and hazel pollen) often also develop a food allergy to pome fruits (such as apples, peaches) and/or nuts (such as hazelnuts and walnuts).
In adults with hay fever, cross-reactions with pome and stone fruits (e.g. apples, plums, nectarines), celery, carrots, crustaceans and shellfish, and wheat are most common.
Many people confuse the terms food allergy and food intolerance in everyday life. However, these are two different diseases: Unlike allergies, an intolerance does not cause the immune system to react.
Instead, in the case of food intolerance, physical processes are disturbed, as a result of which the food in question or a certain component of it cannot be absorbed or processed properly. As a result, symptoms such as abdominal pain and bloating occur.
Known food intolerances are lactose intolerance, fructose intolerance and histamine intolerance.
Celiac disease (gluten intolerance) is considered neither an allergy nor a food intolerance, but an autoimmune disease.
Food allergy: symptoms
Food allergy symptoms can vary – both in type and severity. For example, common symptoms include:
- Itching
- hives (urticaria)
- Sudden reddening of the skin with a feeling of heat, especially on the face and neck (flush)
- swelling of the lips and mucous membranes in the mouth and throat
Sometimes a food allergy also triggers symptoms in the digestive tract, such as nausea, vomiting, abdominal cramps, flatulence, diarrhea or constipation.
In more severe cases, allergic reactions affect breathing and/or the cardiovascular system: There may be spasmodic constriction of the bronchial tubes with shortness of breath, drop in blood pressure, palpitations and even anaphylactic shock.
In the event of anaphylactic shock, there is a danger to life! In case of possible signs, you should therefore call the emergency doctor immediately!
Food allergy: causes and risk factors
How and why some people develop a food allergy is not yet fully understood. However, there is a genetic predisposition to develop allergies. It is called atopy. In interaction with various environmental stimuli, this can then actually develop into an allergy, such as a food allergy:
A primary food allergy developed in this way occurs preferentially in young children. Adults, on the other hand, suffer more frequently from a secondary food allergy – developed as a cross-reaction in pre-existing allergies to inhaled allergens (such as pollen in hay fever).
Different types of allergy
Contact with the allergenic food usually triggers specific antibodies of the immunoglobulin E (IgE) type in those affected. They activate other immune cells, the so-called mast cells. These release the messenger substance histamine, which makes the mucous membranes swell, causes itching and triggers various inflammatory processes in the body. This form of allergic reaction is called type I allergy. It is also called immediate type allergy because the allergic symptoms appear very quickly (e.g. asthma attack).
In addition, there are mixed types of food allergies. Here, one observes both IgE- and T-cell-mediated allergic reactions.
You can read more about the different types of allergic reactions at Allergy – Allergy Types.
Environmental factors
Several factors seem to favor the development of allergies such as food allergy. This applies, for example, to tobacco smoke during pregnancy and excessive hygiene during childhood. The administration of cow’s milk-based infant formula in the first days of life is also apparently unfavorable. Affected babies are more likely to develop a cow’s milk allergy than those who receive a so-called amino acid formula instead. This is an infant formula that contains only the building blocks of proteins – i.e. amino acids.
Based on such observations and studies, experts have developed recommendations for the prevention of allergies. You can read more about this under Allergy prevention.
Food allergy: examinations and diagnosis
Anamnesis
During the anamnesis interview, the physician will inquire in more detail about the symptoms that occur and any temporal correlations with food intake. For this purpose, it can be useful if affected persons (or the parents of affected children) keep a dietary and symptom diary for a while.
An important piece of information for the doctor is also whether the patient himself suffers from hay fever or other allergic diseases. An additional food allergy is then more likely. Allergic diseases in the family should also be reported to the doctor.
Tests
With a food allergy test of the skin, the doctor can test the reaction of the immune system to certain allergens, such as apple components. In what is called a prick test, he or she introduces components of various possible allergens into the patient’s skin through a small incision. If the body reacts to this with a local reddening, this food allergy test is positive.
The determination of specific IgE in the blood helps to diagnose a food allergy in which such antibodies are involved.
The procedure can be very laborious if different test substances are administered in several runs. The result is particularly meaningful if the test is performed in a double-blind placebo-controlled manner. This means that neither the doctor nor the patient knows (double-blind) whether a potential allergen or a placebo is actually being tested in one run.
In the case of severe food allergy, the reaction to the administered allergen can be very severe, up to and including anaphylactic shock. Therefore, caution and careful medical observation are very important during a provocation test. If necessary, the physician must quickly administer medication to the patient to counteract the life-threatening shock.
In some cases, a diagnostic elimination diet (omission diet) is helpful. This involves specifically omitting suspicious foods in order to see to what extent the symptoms improve as a result.
Read more about allergic skin tests, IgE determination and provocation test in the article Allergy test.
Food allergy: Treatment
A problem for allergy sufferers is that most food manufacturers do not provide a complete list of ingredients for their products. However, the most common allergenic foods (such as nuts, eggs, milk or soy) must now be declared on packaging, even if they are only present in trace amounts.
Emergency kit for severe allergy sufferers
People with severe food allergies must always carry an emergency kit. It contains medication in case of a severe allergic reaction after accidental ingestion of the allergen.
- a fast-acting antihistamine, e.g., in the form of a melting (tablet) form
- a glucocorticoid, e.g. in tablet or suppository form
- a preparation containing adrenaline (or epinephrine), which affected persons can inject themselves into the muscle (autoinjector)
For allergy sufferers who have asthma or have experienced seizure-like bronchospasm in the past, the emergency kit should also include a bronchodilator medication for inhalation.
The emergency medication can save the life of the affected person in case of emergency!
Hyposensitization (specific immunotherapy)
This is the case, for example, with a confirmed peanut allergy in minors: after a careful risk-benefit assessment, oral hyposensitization can be considered for them. In many cases, this allows the individual threshold dose of peanut proteins to be increased, above which the affected person reacts with allergic symptoms.
The preparation used for hyposensitization (a powder made from peanut proteins) is approved in the EU and Switzerland for the age group four to 17 years.
If a food allergy is related to a pollen allergy, hyposensitization with pollen allergens can be performed (provided that the pollen-related respiratory symptoms support such treatment). As a positive side effect, the food allergy occurring as a cross-reaction may then also improve. For hyposensitization, physicians administer the respective allergen (pollen proteins) either under the tongue (sublingual immunotherapy) or under the skin (subcutaneous immunotherapy).
Food allergy: course and prognosis
A food allergy that already occurs in infancy and toddlerhood often disappears on its own. Therefore, it is advisable for physicians to use an oral provocation test to check at regular intervals whether the child is still allergic to the food in question:
In the case of cow’s milk, hen’s egg, wheat and soy allergies, for example, the tests should be carried out every six or twelve months. In the case of other food allergies such as peanut, fish or primary tree nut allergy, testing can be carried out at longer intervals to see whether the child’s immune system has meanwhile developed a tolerance (e.g. every three to five years).
A food allergy that develops only in adults is usually permanent.
Food allergy: prevention
The genetic predisposition to allergies (atopy) cannot be prevented. However, it is possible to eliminate or reduce factors that promote the development of allergies such as food allergy.
Children themselves should also enjoy as varied a diet as possible in the first year of life after the introduction of complementary foods (from the 5th to 7th month of life). Ideally, this should also include common allergens such as cow’s milk. To specifically prevent a chicken egg allergy, the little ones should regularly be given heated chicken eggs, for example hard-boiled eggs (but not scrambled eggs!).
Read more about these and other tips for the prevention of allergies such as a food allergy in the article Allergy – Prevention.
