Food allergy

Introduction Foodallergy, also known as foodallergy or allergicreaction of differential system, allergic gastroenteritis, etc., is caused by IgE-mediated and non-IgE caused by certain foods or food additives. Mediates an immune response that leads to an allergic reaction in the digestive system or systemic.

Cause

1. There are five ways to induce allergies in food: gastrointestinal ingestion, respiratory inhalation, skin contact or injection, through human milk and placenta.

2. Food allergens Food allergens refer to food antigen molecules that cause an immune response. Almost all food allergens are proteins, most of which are water-soluble glycoproteins with a molecular weight of 100,000 to 600,000. Each food protein may contain several different allergens. The food has the following characteristics:

(1) Any food can induce allergies: but the common food allergens in children are milk, eggs, and soybeans. Milk and eggs are the most common allergens in children. Allergens are also different depending on the eating habits of each region. . Peanut is not only a common allergen in children but also in adults. Seafood is not a major allergen in children. Nut-induced allergies are rare in children. Although any food can be sensitized, about 90% of allergic reactions are caused by a few foods, such as Milk, eggs, peanuts and wheat.

(2) Only some components of food are allergenic: in milk and eggs, for example, at least 5 kinds of milk have allergenicity, among which casein and beta-lactoglobulin (-LC) The most allergenic. Egg yolks have relatively few allergens. Egg albumin and egg mucin in egg whites are the most common allergens in eggs.

(3) Variability of food allergenicity: Heating can reduce the allergenicity of most foods. An increase in the acidity of the stomach and the presence of digestive enzymes can reduce the allergenicity of the food.

(4) Cross-reactivity between foods: Different proteins may have a common antigenic determinant, making the allergen cross-reactive. If at least 50% of milk allergies are also allergic to goat milk. Those who are allergic to eggs may also be allergic to eggs of other birds. Cross-reaction does not exist between milk and beef, nor between eggs and chicken. The cross-reactivity of plants is more pronounced than that of animals, such as those who are allergic to soybeans, and may also be allergic to other members of legumes such as lentils and mites. Patients with allergies to pollen also respond to fruits and vegetables. For those who are allergic to birch pollen, they also respond to apples, hazelnuts, apricots, cherries, carrots, etc. Those who are allergic to mugwort also respond to umbelliferous vegetables such as celery, fennel and carrots.

(5) Allergic to intermediate metabolites of food: very rare, patients often have symptoms 2 to 3 hours after eating.

3. Genetic factors Food allergies are related to genetics. If one of the parents has a history of food allergies, the child's prevalence rate is 30%. Both parents have the disease, and the child's prevalence rate is as high as 60%.

4. Anatomical factors: The non-specific and specific mucosal barrier system of the human gastrointestinal tract can restrict the invasion of intact protein antigens, and the food antigen entering the intestinal tract combines with secretory IgA (SIgA) to form an antigen-antibody complex, which limits The intestinal absorption of food antigens, thereby directly or indirectly reducing the immune response to food proteins. Pediatric digestive tract mucosa is soft, vascular permeability is high, digestive tract barrier function is poor, various food allergens easily enter the blood through the intestinal mucosa, causing allergic reactions. Infants below 3 months have lower IgA levels, and the number of plasma cells producing SIgA in the lamina propria is less. When the digestion, absorption process and mucosal immune abnormalities, allergens of various foods easily enter the blood through the intestinal mucosa and allergic gastroenteritis occurs.

5. Other factors: Gastrointestinal inflammation is one of the reasons for the increased incidence of intestinal allergies. This is due to gastrointestinal mucosal damage caused by digestive tract inflammation, which increases the permeability of the gastrointestinal mucosa, causing excessive food antigens to be absorbed and allergic reactions occur.

an examination

Related inspection

Radioallergen Adsorption Test (RAST) Blood Routine

The diagnosis of food allergies is first determined based on detailed medical history, skin test or RAST results. If it is suspected to be IgE-mediated, blinding attacks should be excluded if necessary, but those with severe allergic reactions or those with clear diagnosis should not do so. Suspected to be non-IgE-mediated food-induced gastrointestinal disease, the diagnosis requires biopsy before and after the attack, and food exclusion and challenge tests should be performed unconditionally. According to medical history and/or skin test suspected IgE-mediated disease or food-induced enterocolitis, suspected food should be excluded for 1 to 2 weeks. Other gastrointestinal allergic diseases can rule out suspicious food for up to 12 weeks. If the symptoms do not improve, it is unlikely that food allergies cannot be diagnosed based solely on skin tests or RAST for type I food allergies. Many patients are misdiagnosed as food allergies caused by certain foods, and avoid foods that they should not fast. Therefore, blind history of food and food is important for the diagnosis of the cause. It has also been clinically noted that both IgE and non-IgE types can coexist or interconvert, and patients may be allergic to new food allergens at any time.

Differential diagnosis

Symptoms caused by food allergies are diverse and non-specific, and should be differentiated from digestive tract and systemic diseases caused by non-allergic reactions, such as dyspepsia caused by various causes, cholelithiasis, inflammatory bowel disease, celiac disease, and the like.

Adverse reactions caused by eating certain foods cannot be considered food allergies. The concept of abnormal food reactions proposed by the American Society of Allergy and Immunology in 1984 is cited below.

1. Abnormal reaction (abnormal reaction) is a general concept that applies to all abnormal reactions caused by ingested food and/or food additives, including human immune response to food ingredients or additives (IgE-mediated and non-IgE) Mediated immune response) and non-immune side effects such as food intolerance, toxic metabolic, pharmacological and idiosyncratic responses, and abnormal reactions caused by psychosocial factors.

2. Food intolerance means that the abnormal physiological response caused by food and/or additives is a non-immune reaction caused by food or additives (eg, toxic, pharmacological, metabolic, infectious, and other non-immune factors). The abnormal reaction caused by it, the main difference between it and food abnormal reaction is that it does not involve immune response, but it can be involved in the release of inflammatory mediators by mast cells caused by non-immune factors.

3. Food poisoning (poisoning) is a systemic disease caused by eating foods and/or food additives that are contaminated with poisons or are inherently toxic, accumulating to a certain amount in the effect site, and can be classified into bacterial and non-bacterial. Sexual food poisoning two major categories. Toxic substances can come from contaminated microorganisms and the food itself (such as puffer fish, raw fish gallbladder, etc.), but also from other chemicals (such as arsenic mercury, organophosphorus pesticides, etc.). This abnormal response is generally involved without immune factors.

4. Pharmacological food reaction means that the food and its derivatives and/or food additives contain endogenous pharmacological substances (such as caffeine, histamine, etc.), which are produced after the body has reached a certain amount. The pharmacological effects and performance of a certain drug.

5. Foodpseudo-allergy refers to food abnormalities caused by mental and psychological factors. Its clinical manifestations are similar to food allergies, but do not involve the release of chemical mediators mediated by immune mechanisms.

6. Foodallergy/hypersensitivity refers to the immune response caused by food or food additives in some people. Ingestion of a small amount of food can be induced, independent of the physiological role of food and/or food additives, involving the release of chemical mediators caused by immune mechanisms.

Food poisoning, pharmacological side effects and food intolerance generally do not involve the body's immune response, and food allergies are different, clinical should pay attention to distinguish, especially to avoid misdiagnosis of food allergies as food side effects or food intolerance Accepted.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.