Cross Allergy: What it is and why you should know about it

An allergy is an increased sensitivity of the body to certain allergen substances. It can manifest itself in different ways and it can also be caused by different factors. For example, a respiratory or respiratory allergy is expressed by sneezing, runny nose, itchy nose, conjunctivitis. It is caused by aeroallergens: pollen, mold, dust mites, particles of animal skin. Food allergies are the cause. Most often nuts, cereals, eggs, dairy products, seafood. This type usually presents with 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, such as an exclusive respiratory or food allergy. But there are times when a person with pollen intolerance suddenly has an attack after eating a certain product. Or, for example, a person knows for sure that he only reacts to dust, but suddenly, after seafood, he also has a reaction that is exactly reminiscent of an allergic reaction. In such cases, experts talk about cross-allergy. What is a cross allergy, why it occurs and whether it is dangerous - everyone should know, since no one is immune from it.

What is cross-allergy

The mechanism of occurrence and manifestation of allergies, regardless of its type, follows the same principle. Together with food, inhaled air or in any other way, a certain protein enters the human body, which for some reason the immune system perceives as an alien and dangerous body. As a result, immunity begins to defend itself by its characteristic methods and, in response to a suspicious protein, it produces specific antibodies (for example, immunoglobulin type E - IgE). Antibodies begin to interact with the allergen and typical signs of allergy 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, a cross-reaction occurs when the immune system perceives proteins from different sources as identical. That is, with a cross-allergy, the reaction is caused by a product that, according toIn fact, it is not an allergen for the body.

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

Today, scientists do not have enough information to assess how common this type of allergy is in the world. Although specialists from the Robert Koch Institute have 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 a cross-reaction.

Interestingly, according to the observations of experts, the severity of the primary allergy, as a rule, does not affect the intensity of the manifestation of the 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 the primary allergy. Also, over time, signs of a cross-reaction may disappear. It all depends on the functioning of the immune system.

Causes of cross-reactivity

As already mentioned, proteins are the cause of all allergies. 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 allergy to dust mites and reactions to crustaceans and molluscs. 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 lobster, crabs and other seafood. The birch allergen Bet v1 often leads to cross-reactions to hazelnuts and other nuts, apples, stone fruits, carrots, soy as they contain similar proteins. However, people who are allergic to ragweed and wormwood often also get 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. In short, labile proteins, unlike stable ones, can change their structure under certain circumstances. Labile proteins are easily cleaved during heat treatment, inthe process of cooking, under the influence of enzymes contained in human saliva or intestines. For this reason, people who are allergic to pollen may need to boil or bake hazardous foods to prevent cross-reaction to fruits and vegetables. Under the influence of temperature, the allergen protein will be destroyed.

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

Symptoms and diagnosis of cross-allergy

Symptoms caused by a cross-reaction cannot always be distinguished from signs of true allergy. In most cases, cross-allergy causes mild local symptoms, but severe allergic reactions are also possible (especially if a person has eaten a large amount of food dangerous to him). Symptoms may persist from several minutes to several hours after eating such a meal.

Tellingly, in such cases, the symptoms usually manifest as itching and tingling of the lips, tongue, palate, or throat. In addition, urticaria may appear in the mouth area (mainly in areas of the skin that have been exposed to the juice of the allergen product). But, as a rule, these symptoms quickly pass. Less commonly (about 3% of cases), a cross-reaction can cause anaphylactic shock. Sometimes reactions from the gastrointestinal tract or the 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 to the allergen protein, but to the cross-substance. But identifying the major allergen protein makes it possible to compile a list of potentially cross-reactive foods.

To determine which protein is problematic for a person, it is necessary to donate blood for analysis. Modern laboratory techniques make it possible to determine up to 10 different allergens in 1 ml of a patient's blood. Although in some cases up to 3.5 ml of blood serum may be needed.

Variants of the most common cross-reactions

Dust and seafood

Cross-reactivity between chitins (component of the exoskeleton of mollusks and insects). That is, people with dust mite intolerance are more likely to have a reaction to eating crustaceans, since both species are carriers of the cross-reactive protein tropomyosin.

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

Pollen and certain foods

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

Different types of fish

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

Latex and food

Latex is a substance made from the "milk" of the rubber tree. It is from it that medical gloves, balloons, mattresses and much more are made. Latex can cause several types of allergic and non-allergic reactions (irritation). The most common manifestations of latex allergy are urticaria, edema, shortness of breath, sometimes anaphylaxis. Approximately 30% to 50% of people with a latex allergy may experience cross-allergic reactions to certain foods. Bananas, avocados, kiwis, chestnuts, bell peppers most often give a cross reaction. In this case, scientists discovered several types of proteins involved in the cross-reaction at once.

Nuts and peanuts

Allergies to nuts and peanuts often present with life-threatening anaphylactic reactions. Despite the fact that nuts and peanuts belong to different families (the latter is a legume), however, almost 35% of people with a peanut allergy also react to nuts. But interestingly, not all nuts cause the same strong cross-reaction. The most pronounced is manifested in response to the use of walnuts, pecans and hazelnuts. Cashews, Pistachios, Almonds, and Brazil Nuts are much less likely to cross-react.

Peanuts and beans

Often people who are allergic topeanuts, 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 ) for fear of unwanted reactions. However, studies show that 95% of the time, legumes do not cause a cross-reaction in people with peanut allergies. By the way, a few years ago, peanut intolerant people were indeed 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-reactivity between cow's milk and the milk of other mammals, such as goats or sheep. The results of studies have shown that in almost 90% of people with an allergy to cow's milk, goat and sheep products cause similar symptoms. A much lower risk of allergy - about 5% - is associated with the milk of mares and donkeys. These products are less likely to cross-react with cow's milk.

Different animal products

Cross-allergy symptoms are rarely caused by 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 goes for people who are allergic to chicken eggs. In most cases, they can consume chicken meat without any reactions.

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Cross reagent table
Major allergen Cross allergens
Fruits Vegetables Nuts Spices Other products
Tree pollen (most often birch, alder, hazel) Apple, pear, apricot, peach, nectarine, cherry, plum, prunes, kiwi, lychee, persimmon, strawberry Beans, carrots, celery, green pepper, potatoes, tomato, parsnips, peas, lentils, soy Almonds, hazelnuts, walnuts walnut, peanut Anise, basil, cumin, coriander, dill, fennel, marjoram, oregano, paprika, (13 4) parsley, pepper, tarragon, thyme Sunflower seeds
Pollen of grasses and cereals (mainly wheat, rye) Date, kiwi, melon, orange, watermelon Peas and other legumes, potatoes, tomatoes Peanuts Barley, oats, millet, corn, wheat, rye (including including flour from them)
Wormwood (pollen) Apple, melon, orange, peach, tomato, watermelon, mango, grapes, lychee Carrot, celery, green pepper, onion, parsnip - Anise, basil, cumin, coriander, dill, fennel, marjoram, mustard, oregano, paprika, parsley, pepper, tarragon, thyme Chamomile, sunflower seeds, honey
Ambrosia (pollen) ) Banana, melon, watermelon Cucumber, zucchini, tomato
Ash and Olive Pollen Pineapple Horseradish ]
Animal hair Cow's milk, meat, offal
Dust mite Shrimp, crabs, lobsters, snails and other seafood
Latex Banana, avocado, kiwi, pineapple, figs, papaya, apple, cherry, grape, melon, peach Potato, tomato, celery Hazelnut, coconut, pistachios - Chestnut, buckwheat, sesame, chocolate, mushrooms and mold fungus Aspergillus fumigatus
Bird allergens (litter, feathers) Eggs, meat, offal
Cher Number of cats Animal fat

Treatment and prevention of cross-allergy

Any allergy is better to prevent than to treat its consequences. The most reliable prevention of a cross-reaction is to refrain from eating foods at risk. But the presence of 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 at risk should be cooked. The fact is that for the most part they contain rather fragile proteins, the structure of which is destroyed under the influence of heat and gastricacids. This means that even if a person is cross-allergic with raw apples, he can safely consume an apple pie with baked fruit. Most allergy sufferers are fine with boiled, canned, or pickled vegetables. Also, plant foods become less dangerous if they are consumed without the peel.

The only exception to this list would probably be celery, and only for people with a primary allergy to wormwood. This vegetable is dangerous for them both raw and boiled. What can not be said about people with a reaction to birch pollen - boiled celery is harmless for them.

An interesting study was made by German scientists about apples. Experts have found that green fruits are more likely to cause cross-reactions, while red apples are more easily tolerated by allergy sufferers. By the way, to reduce the allergic activity of the fruit, it is enough to clean it and let it lie in the air for a while.

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

Thus, the occurrence of a cross-reaction does not lead to an increase in allergy to the main allergen. But it should be understood that stress, the use of alcohol and certain medications can increase the risk and severity of the reaction.