Food allergy is one of the most common allergic conditions caused by intolerance to compounds in some foods. The manifestations of the disease are diverse: skin symptoms (rashes, itching, urticaria), gastrointestinal disorders (dyspeptic disorders), sometimes systemic anaphylactic reactions are possible. Diagnosis is made by setting up skin allergological tests, studying the patient’s anamnesis and food diary, performing laboratory tests. Treatment consists in the elimination of provoking products from the patient’s diet, the appointment of antihistamines, in rare cases – desensitizing immunotherapy.
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Food allergy is the most common allergopathology, which is due to the significant variety of substances that make up human food. Approximately half of the patients are children under the age of 12, and the prevalence of the disease is decreasing in older people. The more frequent occurrence of the disease in children is explained by contacts with antigens new to the body and increased reactivity during this period of life. In the future, immunological tolerance is developed for most food compounds, and allergy manifestations are much less common. There is a genetic predisposition to the development of this condition, which has a polygenic character. In some cases, intolerance to certain foods persists throughout life and can be complicated by cross-reactions and other allergic conditions (for example, bronchial asthma).
Most cases of the disease are caused by hypersensitivity of the first type, mediated by the release of IgE and activation of tissue basophils. The immediate cause of the pathology is the ingestion of protein compounds into the gastrointestinal tract, which are recognized by the immune system and trigger its abnormal response. A huge number of conditions predisposing to food allergies and body features, some of which are characteristic only for children, have been revealed. This is another reason for the frequent development of an allergic reaction in the child population. Among the most common factors contributing to the occurrence of food intolerance, there are:
- Features of the allergen. Hyperreactivity is more often caused by food antigens that have high immunogenicity and are able to overcome the barriers of the digestive system without degradation (in particular, the aggressive environment of the stomach). Most of them are found in cow’s milk, fish, egg whites, cereals, some fruits (strawberries, citrus fruits) and nuts. About 80% of all cases of the disease are caused by hypersensitivity to these products.
- Genetic factors. The development of intolerance may be due to hereditary and genetic properties of the body. They can be manifested by an increased level of reactivity, abnormal activity of the immune system and other conditions that facilitate the development of allergic reactions.
- Age-related features of the gastrointestinal tract. The occurrence of allergies to foods is facilitated by the high permeability of the walls of the gastrointestinal tract observed in children, low acidity of gastric juice, violations of the composition of the intestinal microflora. These conditions facilitate the contact of the allergen with immunocompetent cells that trigger the allergic process.
The probability of the occurrence of the disease is also affected by the amount of allergen that has entered the body, the nature of the culinary processing of products containing provoking substances. Food intolerance may be a consequence of cross-allergy to plant pollen or household dust. The sensitization of the body is caused by antigens carried through the air, but the reaction can also be initiated by food products having similar compounds in their composition.
In the process of developing a food allergy, sensitization of the body initially occurs – it occurs at the first contact with the allergen. The latter is recognized by immune cells, which, through a series of intermediate reactions, cause the formation of class E immunoglobulins specific to this protein compound. Antibodies of this type have the property of adsorbing on the surface of tissue basophils, remaining there for a long time. Upon repeated admission of the provoking antigen, it binds to IgE, which activate mast cells, causing their degranulation with the release of histamine. This biogenic amine causes the expansion of blood vessels, swelling of tissues, irritation of nerve endings – these changes are manifested by skin itching, urticaria, dyspeptic disorders.
The peculiarity of allergy to food components in infancy is the exclusion of the sensitization stage from the pathogenetic chain of the disease. Antibodies against the allergen enter the child’s body transplacentally or with breast milk from a mother who suffers from intolerance to certain foods. For this reason, it is especially important for women with allergies to control their nutrition during pregnancy and lactation – otherwise there is a risk of developing pathology in the baby. But the duration of such a condition in children is insignificant – maternal antibodies are completely eliminated from the body a few weeks after the cessation of natural feeding.
Symptoms of food allergy
The clinical picture of pathology is quite diverse, statistically, skin symptoms that occur within 2 hours after eating are more often recorded. Itching develops, rashes of various localization, usually of an erythematous nature. Some patients complain of urticaria and other edematous phenomena on the surface of the skin. Depending on the severity of the allergy and the nature of the provoking substance, these symptoms may persist for several hours or days. After that, if there is no contact with the allergen, the skin manifestations usually disappear completely and without a trace. If you continue to use a dangerous product, an allergic reaction is registered again, and each new episode is characterized by more pronounced and severe symptoms.
Food allergies can manifest as gastrointestinal disorders in the first hours after eating allergenic foods. Patients complain of abdominal pain, nausea, sometimes vomiting and diarrhea. With a particularly high allergic readiness of the body, these symptoms can develop already at the time of eating. Dyspepsia is accompanied by swelling of the mucous membranes of the oral cavity, lips, and tongue surface. Sometimes such an allergic process leads to nasal congestion, lacrimation, conjunctivitis, which creates a false picture of pollinosis or intolerance to household dust.
Some foods (peanuts, some types of fish, strawberries) contain allergens that cause severe systemic reactions – angioedema and anaphylactic shock, accompanied by laryngeal spasm and a drop in blood pressure. In patients with bronchial asthma, hypersensitivity to food components can provoke the development of an attack by the mechanism of cross-allergy. A number of patients note the appearance of headaches, increased fatigue and weakness after eating dishes with provoking products.
The most severe complication of food allergy is anaphylactic shock caused by massive degranulation of basophils and the release of a large amount of histamine. It occurs with a predisposition to intolerance to certain foods or with prolonged ignoring of the manifestations of the disease. The continued intake of the allergen into the body leads to a gradual increase in symptoms and eventually provokes the development of shock. If the allergy is accompanied by vomiting or diarrhea, prolonged contact with the antigen can lead to electrolyte disturbances. Other complications include the occurrence of cross-intolerance to pollen antigens or household dust, infection of the skin as a result of scratching and damage.
Food allergy is determined by an allergist-immunologist, while close and confidential contact of the doctor with the patient or his parents is important (with the development of pathology in children). To diagnose the disease, anamnesis data, the results of laboratory and immunological studies, as well as provocative tests are used. The latter should be used only in the case of relatively low reactivity of the body and the ease of allergy manifestations. If there is a risk of systemic reactions (Quincke’s edema or anaphylactic shock), conducting studies involving the patient’s contact with an allergen is prohibited. Confirmation of the diagnosis and determination of the provoking product is carried out according to the following algorithm:
- Examination and anamnesis collection. The patient’s skin is examined to determine the nature and severity of rashes, in controversial cases, a dermatologist’s consultation may be required. The food history is analyzed: it turns out which foods have been consumed in recent days and in what quantity. Based on this, the range of possible allergens is limited, which facilitates further research.
- Laboratory tests. In a general blood test, minor eosinophilia is determined only with severe or repeated episodes of allergies. According to the indications, nasopharyngeal flushes, smears-prints from the conjunctiva are subjected to microscopic examination – eosinophils are also found in them. A biochemical blood test reveals a high level of immunoglobulins of classes E and G.
- Skin allergological tests. To accurately determine the allergen, application tests or a prick test are used. At the same time, standards of antigens that came under suspicion during questioning of the patient are applied to the skin. The development of redness and swelling is a positive reaction and indicates the presence of allergen intolerance.
- Immunological tests. These include the solid-phase enzyme immunoassay (ELISA) and the radioallergosorbent test (RAST). They are carried out to determine the type of provoking antigen with high reactivity of the body, when skin tests are excluded. These tests determine with high accuracy the presence of allergen-specific IgE in the patient’s blood
Differential diagnosis of food allergies should be carried out with other allergic diseases (pollinosis, atopic dermatitis) and skin pathologies (eczema, infectious lesions). With the development of dyspeptic disorders, it is necessary to exclude the risk of food poisoning or other diseases of the digestive system. Sometimes symptoms similar to allergy symptoms may occur due to the use of unusual or exotic dishes. Usually these conditions disappear spontaneously in a few hours and rarely reappear.
Treatment of food allergies
Therapeutic measures in practical allergology include three stages: relief of allergy symptoms, acceleration of allergen elimination and prevention of subsequent contact with it. In case of intolerance to essential foods, desensitizing immunotherapy is used. It is also important to take into account the risk of cross-reactions, so after detecting an allergen, a specialist can limit the consumption of a number of dishes at once. Their exclusion from the diet reliably guarantees the absence of new episodes of food allergies. The main stages of treatment consist of:
Symptomatic therapy. Antihistamines are used in various forms of release – in the form of tablets, syrups (in pediatric practice) and nasal sprays. In most cases, a single dose of drugs of this group is sufficient to completely eliminate the manifestations of food allergies. With a more severe course, their course application may be prescribed by a specialist.
Elimination of allergen from the body. It can be provided both by the appointment of a special hypoallergenic diet and by pharmacological methods. In the case of a recent (several hours) ingestion of a provoking product into the gastrointestinal tract, enterosorbents are effective – activated carbon, polysorb. They bind antigens in the intestinal lumen, preventing them from entering the systemic circulation. If several days have passed after the penetration of allergens, or they have been entering the body for a long time, then their elimination is possible only in a natural way. It can be somewhat accelerated by infusion therapy or the appointment of diuretics.
Allergen-specific immunotherapy (AIT). This stage of treatment is possible only after a full diagnosis of pathology and accurate determination of the provoking antigen. It is prescribed if the list of prohibited products is too extensive, or irreplaceable food components fall into it. AIT consists in the introduction of gradually increasing dosages of the allergen in order to develop immunological tolerance to it.
Prognosis and prevention
The prognosis of food allergies is favorable, especially with the development of the condition in childhood – as the child grows, food intolerance gradually disappears and practically does not manifest itself in the future. In the case of severe reactions to peanuts, seafood and some fruits, quite often patients have to give up their use for life. In addition, they are recommended to carry first aid supplies for anaphylactic shock (for example, a special pen syringe with adrenaline). Prevention is reduced to limiting the use of high–risk allergic products in baby food and during pregnancy, and in the presence of reactions – to their complete withdrawal from the diet.