As a foodie, food allergies are really annoying.

One very ordinary evening, after dinner, Tadpole suffered from vomiting and diarrhea, his body broke out in rashes, he felt itchy and wanted to cry, and he felt as if he had food poisoning.

I ran to the hospital with a sad and angry mood and found out it was an allergy. Fortunately, the doctor prescribed loratadine and I finally recovered.

We often hear the word allergy, and even always on our lips, but what exactly is allergy?

01

What are allergies?

Regarding allergies, it has been clearly explained in high school biology textbooks. It is that the body produces an immune response after the first exposure to an antigen, producing antibodies and memory cells. When exposed to the same antigen again, the body quickly initiates the immune process and causes tissue damage or functional disorders.

The mechanism of allergic reaction, image source author

The immune system is like a patrolling policeman in the body, whose main duty is to catch and eliminate the "bad guys" such as viruses and bacteria that invade the body. When the immune system is too sensitive, allergic reactions are prone to occur, and the sensitivity of the immune system has obvious family genetic tendencies and individual differences.

When an allergic reaction occurs, it occurs quickly and the reaction is also very strong, but it also subsides quickly. In general, allergic reactions do not destroy tissue cells or cause serious damage to tissues. (Of course, there are also serious cases that may lead to anaphylactic shock and endanger life)

Allergies may cause sneezing and runny nose. Image source: hippopx

The clinical symptoms of allergies are mostly itchy skin, erythema or urticaria, which may be accompanied by nausea, vomiting, abdominal pain and diarrhea. Some people also experience pharyngeal edema, chest tightness, shortness of breath and breathing difficulties. Extremely rare but very serious anaphylactic shock is manifested by bronchospasm, heart failure, and a drop in blood pressure to coma and collapse, and even death due to shock within a short period of time.

Skin itching, erythema or urticaria, image source: creativecommons

Common allergies in life include food allergies and drug allergies, and the probability of food allergies in the population is not low. So, which foods are more likely to cause allergies? Why are these foods prone to allergies?

02

Types of food allergens

In medicine, food allergy is also called hypersensitivity reaction, and the antigen that can cause hypersensitivity reaction is called allergen, also known as allergen.

Allergic reactions are caused by allergens invading the human body. These allergens are generally proteins with acidic isoelectric points and are generally water-soluble glycoproteins. What are the characteristics of proteins that can become allergens?

First, the molecular weight is relatively small, 1000-7000kD. Second, it can pass through the mucosal surface and has a certain tolerance to degradation by proteases, acids, and heat.

Among children and adults, more than 90% of allergic reactions are caused by 170 protein-rich foods in 8 categories, including eggs, peanuts, milk, soybeans, wheat, shellfish, fish, nuts, etc.

Image source: hippopx

Milk is one of the common allergenic foods for infants and young children. Studies have found that there are more than 40 kinds of proteins in milk with allergenic potential. Among them, casein, lactoglobulin and whey protein are likely to induce allergies in infants and young children, but are generally ineffective for adults.

Table source: Research Progress on Food Allergens and Detection Technologies

Seafood is another common allergenic food, and people of all ages may be allergic to seafood, with no age specificity. Among them, shrimp and other crustaceans are more common, and their allergens are mainly tropomyosin, a protein found in muscle fibers.

Image source: pexels

The incidence of egg allergy is very high, and among infants and children with food allergies, 35% suffer from egg allergy. Egg allergens are mainly found in egg white, including lysozyme, ovomucoid, ovalbumin and ovotransferrin.

Image source: creativecommons

From the perspective of immunological mechanism, food allergy includes four types. Type I is an IgE (immunoglobulin E)-mediated hypersensitivity reaction (what is immunoglobulin? It is the antibody produced after B lymphocytes proliferate and differentiate into plasma cells after the antigen invades the body); Type II is a cytotoxic hypersensitivity reaction; Type III is an immune complex hypersensitivity reaction; and Type IV is a T cell-mediated delayed hypersensitivity reaction.

Reports of food allergies are common, and the phenomenon of food allergies is becoming more and more common. Is there any way to detect allergens contained in food?

03

Food Allergen Testing

The purpose of food allergen testing is to find out which substances in food can cause allergies, to prevent people who are allergic to these substances from becoming allergic without knowing it, or to detect which substances allergic people are allergic to.

The detection of food allergens can be divided into in vivo diagnosis and in vitro detection. In vivo diagnosis mainly uses skin sensitivity tests or double-blind controlled food stimulation tests to detect whether the allergic population is allergic to food and to which food allergens they react.

Here, we mainly look at how to detect which substances allergic people are allergic to.

One of the detection methods is the skin prick test, in which suspected allergens are pricked on the skin. If the allergen enters the skin, an immune response will occur in the patient's body, causing local capillaries to dilate and permeability to increase, that is, erythema or edema will appear on the pricked skin.

Image source: creativecommons

Another method with a long history is the patch test. Some suspected allergens are applied to the patient's skin. If they are allergens, they will induce an inflammatory reaction, which can be used to infer whether the patient is allergic to the substance. This method can be used to detect contact dermatitis or allergic skin diseases.

In addition, there is another detection method, which is serum-specific IgE determination. The patient's serum is obtained and the total IgE level is tested. A high level indicates that the patient is in an allergic state. Then the allergens in the suspected food are extracted and contacted with the patient's serum. If the serum contains IgE antibodies that can bind to a certain allergen, the culprit of the allergy has been found.

Having said so much, I still hope that everyone has no food allergies and enjoys everything they eat. If you really have a food allergy without knowing it, it is best to remember what you ate and then use this as a clue to determine the allergen!

END

Review expert: Wu Xinsheng, deputy chief physician of the Department of Gastroenterology, PLA 371 Hospital

Tadpole Musical Notation original article, please indicate the source when reprinting

Editor/Heart and Paper