Food allergy

introduction

A special form of food intolerance is referred to as a food allergy or food allergy, which is characterized by a hypersensitivity reaction of the immune system to foods or components of these foods (the food allergens) in the diet.
This specific immune reaction distinguishes food allergy from simple, non-immunological food intolerance, which includes lactose intolerance due to lactase deficiency.

The extent of the allergic reaction and its symptoms can vary greatly from person to person. However, it is characterized by swelling of the entire mucous membrane of the mouth, nose and throat, symptoms of the gastrointestinal tract and rashes. In extreme cases, a food allergy can lead to life-threatening anaphylactic shock. The food allergy is one of the allergies from Immediate type (Type I allergy).

In general, a food allergy can occur at any time and at any age. In many cases, however, it shows up in the first few months of life or between the ages of 15 and 35 for the first time.

What types of food allergies are there?

In principle, you can be allergic to any food, even if some substances cause allergies in more people than others. These can also be substances that are biochemically similar to other substances, for example in terms of their molecular structure. In these special cases one speaks of a cross allergy. In addition, the allergic reactions that are caused by a food allergy can only be classified as symptomatic.

It is not known that a certain food would always trigger the same symptom in different allergy sufferers. A food allergy is usually a type I allergic reaction. This means that the symptoms appear extremely quickly and very acutely after contact with the allergy-causing substance. Reactions that occur hours later are less common.

You may also be interested in this topic: Hazelnut allergy

Allergens

Depending on the age, different foods trigger an allergy. This is how infants and young children react primarily to:

• milk
• soy
• egg
• wheat
• Nuts / peanuts
• Fish and
• Shellfish

Adults, on the other hand, are particularly sensitive to nuts, peanuts, fish and shellfish. Most of the time, however, it is not a question of food allergies in adulthood, in which there has been an antibody - antigen reaction with the food that is not tolerated, but rather a secondary food allergy.

One speaks of a secondary food allergy if the food allergy is triggered by another allergy, such as an allergy to pollen.

In babies and toddlers, milk, soy, egg and wheat allergies “grow together” over time, whereas an allergy to nuts, peanuts, fish and shellfish persists.
However, if a food allergy occurs in adulthood, it will remain a lifelong companion.

Also read on this topic:

• Milk allergy
• Wheat allergy

causes

If there is a food allergy, in contrast to a food intolerance, an immunological reaction occurs. This means that the body's own immune system, which normally protects us from bacteria and viruses, is the cause of the food allergy.

The food allergy is based on an antibody-antigen reaction. The body's own antibodies usually ensure recognition and control of foreign substances and microorganisms. In the context of a food allergy, the antibodies bind to certain proteins in the food (Antigens). This causes an immune reaction of the body, which can be shown with the symptoms explained in more detail below.

It is not known what causes the allergy to develop. Since some people do not develop allergies, while others develop more frequently, it can be assumed that genetic factors also play an important role in the development of allergies.
However, based on the observation that the number of allergy sufferers in the population has been increasing steadily for several decades, a number of hypotheses could be formulated. One of the most important theories is the hygiene hypothesis. This hypothesis assumes that excessive hygiene does not stimulate our immune system to a sufficient extent at a young age. This underload of the immune system is said to favor the occurrence of an allergy.

Other hypotheses concern, among other things, the changed habits of people (with increased stress and a changed diet) and increasing environmental pollution by humans. To date, however, no hypothesis can come close to providing a satisfactory explanation for the allergy phenomenon.
In principle, a food allergy can develop for all foods. Foods that are almost never allergenic are rice, artichokes and green salads. Nevertheless, certain foods or components of these foods are excessively often allergens. These include the protein gluten contained in cereal products, dairy products (especially the lactose they contain), peanuts, egg white, nuts, fish, crustaceans and molluscs and soybeans . It is noticeable that, depending on the age of those affected, different allergens can be identified as triggers of a food allergy.

also read Lactose intolerance

Infants and toddlers, for example, suffer from allergies to staple foods such as cow's milk, soy and wheat.
Young people and adults, on the other hand, are much more likely to suffer from allergies to fruit, vegetables, nuts and spices.

If there is already an immunological hypersensitivity to certain food components, a special form of allergic reaction can come into play: the Cross allergy. This is a reaction to substances that are structurally similar to another allergen. For example, people with an allergy to various pollen and grasses can develop hypersensitivity to certain fruits. Typical cross allergies also exist between latex and fruits such as banana, kiwi and avocado.

Sometimes you are not allergic to the food itself, but to certain ingredients, e.g. the histamine in fresh tomatoes.

Learn more at: Tomato allergy

Frequency distribution

Food intolerances are relatively common. For example, around 10% of the German population suffer from one Lactose intolerance. The food allergy symptoms described here occur much less frequently. 1.5% of adults suffer from a food allergy; food allergies are more common in infants.

Symptoms

Mucous membrane reactions are characteristic, more precisely swelling and itching of the mucous membranes of the mouth, nose and throat, as well as gastrointestinal complaints such as nausea, vomiting, flatulence, cramp-like abdominal pain and diarrhea. In addition, asthmatic complaints can occur with swelling of the bronchial mucous membranes and the resulting shortness of breath. Skin reactions are expressed in rashes and redness (exanthema and eczema), hives and itching. Conjunctivitis of the eyes with redness, swelling and severe itching, as well as increased sensitivity to light, can also occur. Other symptoms can include fever and inflammation of the joints (arthritis).

Symptoms of food allergy typically show up immediately after consuming the food that is hypersensitive to it.

Redness can show up on the skin, too itching can occur. Less common symptoms on the skin include an acute one Hives (acute urticaria) or one Neurodermatitis (Atopic dermatitis).

One speaks of acute hives if it does not last longer than 6 weeks. Patients with acute hives complain of extraordinary itching and visible wheals. The clinical picture is similar to that which occurs after accidentally touching nettles.

If atopic dermatitis occurs due to the food allergy, red, flaky and sometimes weeping eczema are in the foreground, which appear in bursts.

Food allergies are characterized primarily by symptoms of the gastrointestinal tract. Classically, symptoms first appear in places at the beginning of the food passage. This means that initially there may be discomfort in the mouth, such as swelling. A few hours after consumption, nausea and vomiting may occur. Finally there are also cramp-like pains (Colic) and diarrhea are possible, which show up to 6 hours after ingesting the food.

Discomfort with the respiratory tract occurs mainly in the context of an anaphylactic shock.This is the maximum of the hypersensitivity reaction of our immune system and is acutely life-threatening. In the course of anaphylactic shock, shortness of breath is in the foreground.

Chronic asthma can also be traced back to a food allergy in around 10% of cases.

It is also worth mentioning that various factors are known which can exacerbate the symptoms of a food allergy. These primarily include psychological stress, physical exertion and the consumption of alcohol.

If infants and toddlers suffer from a food allergy over a long period of time, this can manifest itself in a growth disorder. In such cases, a deviation from the age-typical size and age-specific weight can be seen. It is important that in such cases a pediatrician is consulted so that it can be found out what the real cause of the stunted growth is.
Read our article on this:

• You can recognize histamine intolerance by these symptoms
• Symptoms of an allergy

Diarrhea with a food allergy

A symptom that occurs very often in the context of food allergies is diarrhea (Diarrhea), which occurs about one to two hours after consumption of the respective allergen. It is usually preceded by signs of illness such as nausea and cramp-like abdominal pain. The diarrhea itself is usually very thin, as the intestinal passage which is too short does not allow sufficient water absorption through the colon mucosa. However, the consistency of the diarrhea can also be different and thus possibly be informative about the causative food allergen. So the sprue triggered by the adhesive protein gluten (also Celiac disease called) characterized by mushy, foul-smelling diarrhea. Treatment of the diarrhea should primarily be the cause. Ultimately, this means that the person affected largely renounces the food allergens that are specific to him.

Read more about this under Causes of diarrhea

Food allergy rash

From a rash (Rash) around half of all food allergy sufferers are affected. It is therefore the most common symptom of the food allergy. The skin symptoms typical of a food allergy can be diverse and range from extensive reddening of the skin to swelling (Edema), fine-bubble rash up to hives (Urticaria). Treatment of the rash is possible, but usually not necessary, as it is self-limiting with the excretion of the responsible allergen and thus subsides within hours to days. If therapy is nevertheless desired, this can be done by applying an ointment containing cortisol.

Food allergy pimples

Even if the exact mechanisms are not yet known, the skin can be affected in many ways by an allergy. An allergic reaction can also promote the development of pimples or other skin blemishes. This fits the hypothesis that inflammatory messenger substances are released in the event of an allergic reaction. These can then also contribute to the development of skin impurities. A good indication of the development of skin blemishes due to a food allergy is that the skin blemishes decrease as soon as the suspicious food is no longer eaten for some time.

diagnosis

When diagnosing a food allergy, a detailed anamnesis is the top priority. A diary, in which the food eaten and the patient's complaints, can be helpful.

It is also important to remove the suspected food from the menu for a while. The symptoms should subside within 2 weeks.

Your family doctor, dermatologist or allergist can investigate your suspicions using a skin test, the so-called prick test.

In rare cases, a so-called provocation test can be used. As part of the provocation test, the body is provoked, so to speak, which means that the food that is not tolerated is explicitly consumed. It is important that this only takes place under medical supervision, as it can lead to severe anaphylactic reactions that can be fatal.

Further information: Allergy diagnostics

Is there a blood test for a food allergy?

Normally, a food abstinence test should suffice to diagnose a food allergy: This means avoiding the suspected food for a while and analyzing whether this avoidance has a positive, i.e. soothing effect on the allergic symptoms. If this method does not give a sufficiently good result, a blood test can also be carried out.

To do this, the person's blood usually has to be sent to a laboratory, where it is then examined for so-called type E immunoglobulins. These immunoglobulins play a crucial role in the development of an allergic reaction, and there are also specific immunoglobulins of this type for different molecules, if there is an allergy to these molecules. By determining these subspecies of immunoglobulins, a food allergy to certain foods can then be secured.

Also read the article on the subject: Testing for a food allergy

Allergy test

There are several ways to diagnose a food allergy. The simplest, but at the same time most effective option is to keep a nutrition and complaint diary. This makes it possible to establish a direct temporal connection between the consumption of a potentially allergenic food and the subsequent signs of illness. If a certain food is suspected of being the trigger for an allergy, an exclusion diet for several weeks followed by a provocation diet.

Another option for diagnosing a food allergy is to carry out various tests. The so-called prick test, which is also used for other forms of allergy, is very common. Special solutions that contain the suspected allergens are dropped onto the skin and placed under the skin's epidermis through a lancet. At the same time, so-called blank tests are carried out in which a positive control is carried out by introducing histamine and a negative control is carried out by introducing a pure saline solution into the skin. The first skin reactions can be assessed after about a quarter of an hour. In the event of a positive reaction, localized reddening typically occurs, which is limited to the test area, and itching and wheals usually occur.

The third common method used to test for food allergies is blood tests. The easiest way to do this is simply to test for free IgE antibodies. This subgroup of antibodies is produced specifically in the context of allergic reactions and when lymphocytes are infected with parasites. However, this gives rise to the problem that false positive test results can be obtained if the test person is infected by a parasite such as a tapeworm.

Certain haematological diseases such as IgE plasmacytoma can also lead to an increase in IgE levels. Nowadays, however, allergen-specific IgE antibodies can also be measured, the values ​​of which cannot be falsified by other diseases. In addition to these laboratory tests, however, a wide range of new blood tests for diagnosing food allergies are now also available. In addition, the tried and tested measurement of various inflammatory parameters of the blood continues to be used. Above all, the tissue hormone histamine should be mentioned, which is released as part of an allergic reaction and is responsible for many of its symptoms. The enzyme tryptase and the so-called leukotrienes are also increased in an allergic reaction, so that they too can provide information about the general presence of a food allergy.

It should be noted, however, that blood tests are also offered, which in themselves are not suitable for diagnosing a food allergy. For example, Deutsches Ärzteblatt was very critical of the so-called ALCAT test method, which is based on the determination of non-allergy-specific IgG antibodies.

More on this: Allergy test

therapy

Avoiding the corresponding foods is crucial for the therapy of food allergies.
However, in some cases, this is easier said than done. Potential allergens such as gluten and lactose, which are widespread in our society, make it extremely difficult for allergy sufferers to lead a varied diet. This can only be seen from the fact that food allergy sufferers have an incident every third year on average.
Because of this fact, it can be vital for severely affected people to always carry an allergy emergency kit with them. This usually contains an antihistamine in the form of drops or tablets, a cortisone preparation and an automatic syringe with adrenaline. In addition, allergological training or advice from a nutritionist can be useful and helpful.

An example of a particularly serious allergic reaction is peanut allergy, which can lead to anaphylactic shock. For this reason, affected allergy sufferers should be particularly careful and careful with their allergy, as peanuts are not always obvious as a food component. For example, peanuts can also be found in ice cream, muesli, etc. However, there must be an indication on the packaging that the food contains peanuts.

People with other allergies should also avoid certain foods, as these can lead to cross-reactions / cross-allergies.
For example, patients with a birch pollen allergy often cannot tolerate apples and nuts.

There are a few measures that pursue the goal of causal therapy, i.e. aim to treat the cause. This includes, for example, oral tolerance induction under medical guidance and the attempt at subcutaneous desensitization, as is the case with other forms of allergy. The actual benefit of these therapeutic approaches has not yet been fully clarified.

There are also recommendations on how to prevent food allergies. It seems to make sense here to pay attention to a varied food preparation, since the frequent contact with an allergen can generally lead to a sensitization for it. In addition, it has long been known that children who were exclusively breastfed as infants suffer less from allergies than children who are not breastfed. Breastfeeding is therefore a good way of prevention.

Please also read our articles on this:

• Food allergy therapy
• Allergy to apples

Which doctor treats a food allergy?

A doctor from any specialty should be able to provide help for short-term treatment of the symptoms caused by the food allergy. Of course, it depends here on whether the symptoms are severe or even life-threatening - accordingly, a call to the medical emergency service may be more an option than a visit to the family doctor. However, if a food allergy is to be treated over the long term due to severe and sometimes unavoidable symptoms, an allergist can carry out a desensitization. This is intended to weaken the allergy or the corresponding symptoms on contact with the respective substance in the long term.

Duration of the allergic reaction

Food allergies, like grass and pollen allergies, fall into the category of allergies from Immediate type (Type I allergy), the most common form of allergy. This is in itself characterized by a very rapid onset of symptoms within seconds to minutes. Nonetheless, the first symptoms of a food allergy can only become noticeable up to two hours after eating. The reason for this lies in the fact that the so-called Ingestion allergens often only released and absorbed by the body during the digestive process. The duration of the symptoms then varies greatly and can be hours to a few days, depending on the symptom and the individual.

Food allergy in the baby

Infants and toddlers are usually particularly badly affected by food allergies and suffer much more from diarrhea and vomiting than adolescents and adults. This is also often accompanied by an impairment of normal development, especially when it comes to height and weight gain. So are children who are under Celiac disease (a food allergy to gluten), mostly smaller than their peers. Babies and children are typically affected by different allergies than adults. In particular, staple foods such as gluten, lactose, eggs and increasingly soy are typical allergens for infancy. In the case of severe sensitizations, there may even be an allergy to breast milk, as it can contain all allergens that the mother ingests with the food .

The optimal nutrition of newborns consists exclusively of breast milk for at least the first four months of life, whereby the breastfeeding mother should possibly avoid risk foods for the above-mentioned reason. Apart from that, it is special for babies who cannot be breastfed hypoallergenic food available, so-called HA food. However, their disadvantage is a very bitter taste. Soy-based baby food is definitely not recommended because soy is potentially allergic.

In fact, many children who suffered from food allergies in infancy and toddlerhood very often outgrow their allergies by the age of five. Nevertheless, these children seem to have a predisposition to allergic diseases, so that sensitizations (e.g. to pollen) or the occurrence of a bronchial asthma are not unlikely in later life.