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Cross-allergy: what it is and why you should know about it

Allergy is an increased sensitivity of the body to certain allergenic substances. It can manifest itself in different ways and it can also be caused by different factors. For example, respiratory, or respiratory allergy, is expressed by sneezing, runny nose, itching in the nose, conjunctivitis. It is caused by aeroallergens: pollen, mold, dust mites, particles of animal skin. The cause of food allergies are food. The most common nuts, cereals, eggs, dairy products, seafood. This type is usually manifested by swelling of the lips, tongue and throat, urticaria, itching and even anaphylactic shock. Another type of allergy is atopic dermatitis, which occurs as a reaction to touching allergens. There is also an allergy to insect bites and medications.

Many suffer from only one type of allergy, for example, exclusively respiratory or food. But there are cases when a person with pollen intolerance suddenly starts having an attack after eating a certain product. Or, for example, a person knows for sure that he reacts only to dust, but suddenly, after seafood, he also has a reaction that is exactly like an allergic reaction. In such cases, experts talk about cross-allergy. What is cross-allergy, why it occurs and whether it is dangerous - everyone should know. After all, if you believe the experts, by and large no one is immune from it.

What is cross-allergy?

The mechanism of occurrence and manifestations of allergy, regardless of its type, is based on one principle. Together with food, inhaled air or any other way, a certain protein penetrates the human body, which for some reason the immune system perceives as an alien and dangerous body. As a result, immunity by the methods characteristic of it begins to defend itself from a stranger. In response to a suspicious protein, it produces a specific antibody (for example, an immunoglobulin of type E - IgE). The antibody begins to interact with the allergen and typical allergy symptoms appear.

Cross-allergy is a kind of phenomenon. It appears when the immune system mistakenly reacts not to the allergen protein itself, but to another - structurally similar to it. In other words, cross-reaction occurs when the immune system perceives proteins from different sources as an identical substance. That is, with cross-allergy, a reaction causes a product that, in fact, is not an allergen to the body.

For example, people with primary allergies to birch pollen can also react to raw apples, peaches, carrots, peanuts, or hazelnuts. And all because these products contain protein, structurally similar to that contained in birch pollen, and that for such people is already an allergen.

At present, scientists do not have enough information to assess how common this type of allergy is in the world. Although experts from the Robert Koch Institute calculated that, for example, in Germany, about 6 out of 10 cases of allergies in children are a cross reaction. But as scientific observations have shown, people with a strong allergy to birch pollen are still most at risk of cross-reaction.

What is interesting, according to the observations of experts, the severity of the primary allergy, as a rule, does not affect the intensity of the manifestation of cross-reaction. Often, primary allergies cause only mild symptoms, while cross-reactions are much more severe. And one more interesting fact. Cross-allergy is not a congenital disorder. It can develop many years after the first manifestation of primary allergy. Also, over time, signs of cross-reaction may disappear. It all depends on the work of the immune system.

Causes of cross reaction

As already mentioned, the cause of any allergies are proteins. The main triggers of cross-reactions are usually called pollen, dust mites, animal hair and proteins that enter the human body along with them.

From a biological point of view, there is an interesting relationship between dust mite allergy and the reaction to crustaceans and mollusks. Since dust mites, like crustaceans, belong to the type of arthropods, their organisms contain similar proteins. Therefore, some people who are allergic to house dust have a cross-reaction to lobsters, crabs and other seafood. The Bet v1 birch allergen often leads to cross-reactions to hazelnuts and other nuts, apples, stone fruits, carrots, soybeans, as they contain similar proteins. But people who are allergic to ambrosia and wormwood, often also receive reactions to celery, spices, cucumbers, melons, bananas.

Whether a protein will cause an allergic reaction depends on two factors: its structure (stable or labile) and the amount in the food product. In short, labile proteins, in contrast to stable proteins, in certain circumstances, can change their structure. Labile proteins are easily split by heat treatment, in the process of cooking, under the influence of enzymes contained in human saliva or intestines. For this reason, people who are allergic to pollen, to prevent cross-reactions to fruits and vegetables, it is enough to boil or bake dangerous products. Under the influence of temperature, the allergen protein will collapse.

Stable proteins enter the bloodstream in a more or less intact form and usually cause systemic reactions in an allergic person. But proteins prone to lability usually provoke exclusively local reactions.

Symptoms and diagnosis of cross-allergy

Symptoms caused by cross-reaction can not always be distinguished from signs of a real allergy. In most cases, PA causes mild local symptoms, but severe allergic reactions are also not excluded (especially if a person has eaten a large amount of food that is dangerous for him). Symptoms can persist from a few minutes to several hours after consuming such a meal.

Characteristically, in such cases, the symptoms usually manifest as itching and tingling of the lips, tongue, palate or throat. In addition, in the area of ​​the mouth may appear urticaria (mainly in areas of the skin, which got the juice of the allergen product). But, as a rule, these symptoms quickly pass. Less frequently (in about 3% of cases), cross-reaction can cause anaphylactic shock. Sometimes reactions from the gastrointestinal tract or cardiovascular system are possible.

It is very difficult to diagnose cross-allergy, as well as to accurately determine the list of reagent products. During testing, a positive reaction may occur not directly on the allergen protein, but on the cross-substance. But the definition of the main protein-allergen makes it possible to make a list of products that potentially cause a cross-reaction.

To determine which protein is problematic for a person, it is necessary to donate blood for analysis. Modern laboratory techniques can detect up to 10 different allergens, having only 1 ml of patient's blood. Although in some cases you may need up to 3.5 ml of serum.

Variants of the most common cross reactions

Dust and seafood

Proved cross-reactivity between chitin (component of the exoskeleton of mollusks and insects). That is, people with intolerance to dust mites are likely to react to the use of crustaceans, since both species are carriers of the cross-reactive type of tropomyosin.

There is a high degree of cross-reactivity in response to the consumption of different kinds of seafood (shrimps, lobsters, crabs, crayfish). That is, if a person has an allergy, for example, to shrimp, then the risk of reaction to other crustaceans is about 75%. This percentage is slightly lower between crustaceans and mollusks, such as oysters, scallops, mussels.

Pollen and some food

Some people who are allergic to pollen (allergic rhinitis, hay fever) may have unpleasant symptoms after eating raw fruits, vegetables, nuts or seeds containing proteins that cross-react to pollen. For example, people allergic to alder pollen react to apples, peaches, pitted fruits, carrots, peanuts, and hazelnuts. For people who are allergic to ambrosia, unwanted symptoms can cause melon. By the way, the same fruit, but different varieties can be differently tolerated by an allergic. For example, in a person who is allergic to pollen, one sort of apple can provoke a strong cross reaction, while the fruit of another variety can consume it with little or no consequence.

Different types of fish

Specialists have many facts confirming the existence of cross-allergy caused by different types of fish. If a person is allergic to one of the fish species, then the likelihood that other fish species will also provoke an adverse reaction is more than 50%.

Latex and food

Latex is a substance made from the "milk" of a rubber tree. Medical gloves, balloons, mattresses and much more are made from it. Latex can cause several types of allergic and non-allergic reactions (irritation). Most often, an allergy to latex is manifested by urticaria, edema, shortness of breath, and sometimes - anaphylaxis. Approximately 30% to 50% of people who are allergic to latex may experience a cross-allergic reaction to certain foods. Most often, cross-reaction give bananas, avocados, kiwi, chestnuts, bell peppers. In this case, scientists have discovered several types of proteins involved in cross-reaction.

Nuts and Peanuts

Allergies to nuts and peanuts are often manifested by life-threatening anaphylactic reactions. Although nuts and peanuts belong to different families (the latter is representative of legumes), almost 35% of people allergic to peanuts also react to nuts. But interestingly, not all nuts cause an equally strong cross-reaction. The most pronounced is manifested in response to the consumption of walnuts, pecans and hazelnuts. Cashews, pistachios, almonds and Brazil nuts cause a cross reaction much less often.

Peanuts and beans

Often, people who are allergic to peanuts, having learned that this is not a nut at all, but a representative of legumes, exclude other products from this group from their diet (beans, beans, soybeans, lentils), fearing an undesirable reaction. Nevertheless, studies show that in 95% of cases, legumes do not cause cross-reactions in people with peanut allergy. By the way, a few years ago, those who did not tolerate peanuts were really advised to avoid legumes, but as it turned out later, this is not necessary.

Milk of cows and other mammals

There is a high degree of cross-reaction between cow's milk and the milk of other mammals, such as goats or sheep. Research results have shown that in almost 90% of people who are allergic to cow's milk, goat and sheep products cause similar symptoms. Much lower risk of allergies - about 5% - is associated with the milk of mares and donkeys. These products are less likely to cross-react with cows milk.

Different animal products

Signs of cross-allergy rarely cause products from the same group of animals. In other words, if a person is allergic to cow's milk, then in most cases he can eat beef without consequences. The same applies to people who are allergic to chicken eggs. In most cases, they can eat chicken without any reactions.

Cross-Reagent Table
Main allergenCross-allergens
FruitsVegetablesThe nutsSpiceOther products
Pollen of trees (most often birch, alder, hazel)Apple, pear, apricot, peach, nectarine, cherry, plum, prune, kiwi, lychee, persimmon, strawberryBeans, carrots, celery, green peppers, potatoes, tomatoes, parsnips, peas, lentils, soyAlmond, hazelnut, walnut, peanutAnise, basil, cumin, coriander, dill, fennel, marjoram, oregano, paprika, parsley, pepper, tarragon, thymeSunflower seeds
Pollen of herbs and cereals (mainly wheat, rye)Date, Kiwi, Melon, Orange, WatermelonPeas and other legumes, potatoes, tomatoesPeanut-Barley, oats, millet, corn, wheat, rye (including flour from them)
Wormwood (pollen)Apple, melon, orange, peach, tomato, watermelon, mango, grapes, lycheeCarrots, celery, green pepper, onion, parsnip-Anise, basil, cumin, coriander, dill, fennel, marjoram, mustard, oregano, paprika, parsley, pepper, tarragon, thymeChamomile, sunflower seeds, honey
Ambrosia (pollen)Banana, melon, watermelonCucumbers, zucchini, tomatoes---
Ash and olive pollenA pineappleHorseradish---
Animal hair----Cow milk, meat, offal
Dust mite----Shrimps, crabs, lobsters, snails and other seafood
LatexBanana, avocado, kiwi, pineapple, fig, papaya, apple, cherry, grape, melon, peachPotato, Tomato, CeleryHazelnut, coconut, pistachios-Chestnut, buckwheat, sesame, chocolate, mushrooms and mold Aspergillus fumigatus
Avian allergens (litter, feather)----Eggs, meat, offal
Wool cats----Animal fat

Treatment and Prevention of Cross Allergy

Any allergy is better to prevent than to treat its effects. The most reliable prevention of cross-reaction - to refrain from the use of products from the risk group. But having a reaction to a certain allergen is not a guarantee that a person will react to all products from the “dangerous” list.

To avoid cross-allergy, products from the risk group must be subjected to heat treatment. The fact is that for the most part they contain rather fragile proteins, the structure of which is destroyed by heat and gastric acids. This means that even if a person has a cross-allergy caused by raw apples, he can safely consume apple pie with baked fruit. Most allergy sufferers normally tolerate boiled, canned, or pickled vegetables. Also, herbal products become less dangerous if consumed without skin.

The exception from this list will be, perhaps, only celery and only for persons with the main allergy to wormwood. To them this vegetable is dangerous both in its raw and cooked form. What will not tell about people with a reaction to birch pollen - for them boiled celery is harmless.

An interesting study German scientists have done about apples. Experts have found that the cross-reactions often cause fruit of green varieties, while red apples are more easily tolerated by allergies. By the way, to reduce the allergic activity of the fruit, it is enough to clean it and let it sit for a while in the air.

As a rule, products that cause cross-reactions with pollen are most dangerous for allergy sufferers during the period of flowering of the allergen plant. In other seasons, such food may not cause any adverse reactions.

Thus, the occurrence of cross-reaction does not lead to increased allergies to the main allergen. But it should be understood that stress, alcohol and certain drugs may increase the risk and severity of the reaction.

Article author:
Furmanova Elena Alexandrovna

Specialty: pediatrician, infectious diseases specialist, allergist-immunologist.

Total experience: 7 years.

Education: 2010, SSMU, pediatric, pediatrics.

Experience infectious diseases more than 3 years.

He has a patent on the topic “A method for predicting the high risk of the formation of a chronic pathology of the adeno-tonsillar system in frequently ill children”. As well as the author of publications in the journals of the Higher Attestation Commission.

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