Allergic reactions: what is it, symptoms, causes, treatment

general information

Allergic reactions (hypersensitivity reactions) are an inadequate response of the immune system to usually harmless substances.

Usually, the immune system, which includes antibodies, white blood cells, mast cells, complement proteins, and other substances, protects the body from foreign substances (called antigens). In susceptible individuals, the immune system may overreact to certain substances (allergens) in the environment, food or drugs that are harmless to most of people. The result is an allergic reaction. Some people are allergic to only one substance. Others may be allergic to several substances. In Russia, about a third of the population has allergies.

Allergens can cause an allergic reaction if they come into contact with the skin, eyes or respiratory tract, through food, or by injection. An allergic reaction can happen in several ways:

• As seasonal allergies (e.g. hay fever) caused by exposure to substances from trees, grass or pollen.
• Allergies can be caused by taking a drug (drug allergy)
• Allergies can be caused by eating certain foods (food allergy)
• Allergies can be caused by inhalation of dust, animal hair, or mold (year-round allergies)
• Allergies can be caused by contact with certain substances (such as latex)
• Allergies can be caused by insect bites (can lead to anaphylactic reactions and angioedema)

In many allergic reactions, upon first contact with an allergen, the immune system produces a type of antibody called immunoglobulin E (IgE). In the bloodstream, IgE binds to a specific type of white blood cell called basophils, and in tissues it binds to a similar type of cell called mast cells. The first contact with an allergen can make people susceptible to it (a phenomenon called sensitization), but it does not cause symptoms. When people with hypersensitivity come into contact with the allergen again, basophils and mast cells, which have on their IgE surfaces, release substances (histamine, prostaglandins and leukotrienes) that cause swelling and inflammation of the surrounding fabrics. These substances trigger a cascade of reactions that continue to irritate and damage tissues. These reactions range from mild to severe.

- Sensitivity to latex.

Latex is obtained from the sap of a rubber tree. It is used to make rubber products, including rubber gloves, condoms, and medical equipment such as catheters, breathing tubes, enema tips and dental protectors gaskets.

Latex can cause allergic reactions, including an allergic rash (urticarial rash) and even severe and potentially life-threatening allergic reactions called anaphylactic reactions. However, the dry and irritated skin that many people experience after wearing latex gloves is usually the result of irritation rather than an allergic reaction to latex.

In the 1980s. healthcare workers have been advised to use latex gloves for all contact with patients to prevent the spread of infections. Since latex allergy occurs more and more frequently among health care workers.

In addition, the risk of developing sensitivity to latex may be increased if:

• carrying out several surgical procedures;
• the need to use a catheter to assist with urination;
• work in factories that manufacture or distribute latex products.

For unknown reasons, people with latex allergies are often allergic to bananas and sometimes other foods such as kiwi, papaya, avocado, chestnuts, potatoes, tomatoes, and apricots.

Doctors may suspect latex allergy based on symptoms and the patient's description of the circumstances of the symptoms, especially if the patient is a healthcare professional. Sometimes a blood test is done to confirm the diagnosis, or skin tests.

People who are allergic to latex should avoid it. For example, healthcare workers may use gloves and other latex-free products. These products are available in most healthcare facilities.

Allergy Causes

The combination of genetic and environmental factors contributes to the development of allergies.

It's believed that genes have a certain effect, since people with allergies are characterized by common specific mutations; in addition, there is a familial predisposition to allergies.

Environmental factors also increase the risk of developing allergies. These risk factors include the following:

• repeated contact with foreign substances (allergens);
• food ration;
• pollutants (such as tobacco smoke and exhaust fumes).

On the other hand, contact with various bacteria and viruses during childhood can strengthen the immune system, help the immune system learns to respond to allergens in a harmless way and thus help prevent the development of allergies. An environment that limits your child's exposure to bacteria and viruses, which is generally considered beneficial, can increase the likelihood of developing allergies. Contact with microorganisms is limited in families with fewer children, living in cleaner rooms and starting antibiotic use early.

Microorganisms live in the digestive tract, in the respiratory tract and on the skin, but their composition varies from person to person. The presence of certain microorganisms, apparently, affects the appearance and development of allergies.

Allergens most commonly associated with allergic reactions include:

• house dust mite excrement;
• dandruff of animals;
• pollen (trees, grasses and weeds);
• mold fungi.

Household dust mites live in dust that accumulates in carpets, bedding, upholstered furniture and stuffed animals.

Allergy symptoms

Most allergic reactions are mild, like watery eyes and itchy eyes, runny nose, itchy skin, and sneezing. A rash often appears (incl. urticaria), accompanied by itching.

Hives- These are small, red, slightly raised areas (blisters), often with a light center. Swelling may occur in larger areas under the skin (angioedema). Edema is caused by fluid leakage from the blood vessels. Quincke's edema can have serious consequences depending on which parts of the body are affected.

Allergies can trigger seizures asthma.

Some allergic reactions, the so-called anaphylactic reactionscan be life-threatening. Narrowing (squeezing) of the airways may occur, causing wheezing; also, the lining of the throat and airways may swell, making it difficult to breathe. Blood vessels can dilate (dilate), causing a dangerous drop in blood pressure.

Diagnostics

Diagnostics may include:

• medical examination;
• blood tests;
• skin tests and allergen-specific serum IgE test.

Doctors first determine if the reaction is allergic. They can ask the following questions:

• Does the patient have any close relatives with allergies, since in such cases the reaction is most likely to be allergic?
• How often do reactions occur and how long do they last?
• How old was the patient when the reactions began?
• Is there a factor causing the reaction (such as exercise or contact with pollen, animals, or dust)?
• Have any treatments been tried, and if so, what was the patient's response to them?

Blood tests are sometimes done to look for a type of white blood cell called eosinophils. Although everyone has eosinophils, they are usually produced in large quantities when an allergic reaction occurs.

Since each allergic reaction is caused by a specific allergen, the main purpose of diagnosis is to identify that allergen. Often, the patient and the doctor can determine the allergen based on when the allergy started, when and how. reactions often occur (for example, at certain times of the year or after consuming certain products).

Skin tests and allergen-specific serum IgE tests can also help doctors identify a specific allergen. However, these tests may not detect all allergies, and sometimes they show that a person has allergic to any allergen, although in fact it is not (the so-called false positive result).

- Skin tests.

Skin tests Is the most useful way to identify specific allergens.

Usually do first scarification skin test. For this, solutions are prepared from extracts of pollen (from trees, grasses or weeds), fungal mold, house dust mites, animal hair, insect poison, food and some antibiotics. A drop of each solution is placed on the human skin and pricked with a needle.

Doctors may also use other solutions to help interpret allergen reactions. A drop of histamine solution, which should cause an allergic reaction, is used to determine the function of the patient's immune system. For comparison, a drop of a solvent is used, which should not cause an allergic reaction.

If a person is allergic to one or more of these allergens, then he or she develops a bloom-type skin reaction characterized by the following symptoms:

• Within 15–20 minutes, a pale, slightly raised swelling called a papule appears at the site of the prick.
• The resulting papule is about 1/8 to 2/10 inches (about 0.3 to 0.5 cm) larger than the diameter of the solvent papule.
• The papule is surrounded by a clearly defined area of ​​redness - hyperemia.

Most allergens can be detected with a skin prick test.

If the allergen is not identified, it is carried out intradermal test. In this test, a small amount of each solution is injected into the human skin. This type of skin test is more likely to detect an allergen reaction.

Before getting skin tests done, patients are asked to stop taking antihistamines and certain antidepressants. which are called tricyclic antidepressants (for example, amitriptyline), as well as monoamine oxidase inhibitors (for example, selegiline). These drugs can suppress the skin test reaction. Some doctors also do not test patients who are taking beta-blockers, because if such people have an allergic reaction to the test, the consequences can be serious. In addition, beta blockers can interfere with medications used to treat severe allergic reactions.

- Allergen-specific tests with serum IgE.

An allergen-specific serum IgE test (blood test) is used when skin tests cannot be done, for example, when a rash spreads throughout the body. This test can determine if IgE in a person's blood binds to a specific allergen used for the test. If binding is observed, then the person is allergic to the allergen being tested.

- Provocative test.

When conducting a provocative test, people are directly exposed to the allergen. This test is usually done when a person has to document their allergic reaction, for example, to pay for sick leave. It is sometimes used to diagnose food allergies. If doctors suspect exercise-induced allergies, they may ask the person to do exercise.

Allergy treatment

Treatment may include:

• avoiding contact with the allergen;
• antihistamines;
• mast cell stabilizers;
• corticosteroids;
• allergen-specific immunotherapy;
• in case of severe allergic reactions, emergency treatment is required.

The best way to treat and prevent allergies is to avoid the allergen.

When mild symptoms appear, they are usually treated with antihistamines. If they are not effective, other medications, such as mast cell stabilizers and corticosteroids, may help. Non-steroidal anti-inflammatory drugs (NSAIDs) are not beneficial except eye drops used to treat conjunctivitis.

Serious symptoms, such as those affecting the airways (including anaphylactic reactions), require urgent treatment.

- Antihistamines.

Antihistamines are most commonly used to relieve allergy symptoms. Antihistamines block the action of histamine (which causes symptoms). They do not stop the body's production of histamine.

Taking antihistamines helps with runny nose, watery eyes, itching, and reduces swelling caused by hives or mild angioedema. But antihistamines do not make breathing easier when the airway is narrowed. Some antihistamines (such as azelastine) are also mast cell stabilizers.

Antihistamines come in the following forms:

• tablets, capsules, liquid solutions for oral administration;
• nasal aerosols;
• eye drops;
• lotions or creams.

The dosage form of the drug taken depends on the type of allergic reaction. Some antihistamines are available over the counter (over the counter) and some require a prescription. Some drugs that were previously sold as prescriptions are now available without a prescription.

Antihistamines and vasoconstrictors (such as pseudoephedrine) are also available over the counter. They can be used by adults and children aged 12 and over. Such preparations are particularly useful for achieving antihistamine and nasal vasoconstrictor action. However, for some patients, for example, those taking monoamine oxidase inhibitors (a type of antidepressant), these drugs are contraindicated. Also, vasoconstrictor drugs are not recommended for patients with high blood pressure, unless it is done on the recommendation and under the supervision of a physician.

The antihistamine diphenhydramine is available over the counter as a lotion, cream, gel, or spray to be applied to the skin to relieve itching, but should not be used. Its effectiveness has not been proven, and it can also cause allergic reactions (such as rashes). It can cause severe drowsiness in children taking it by mouth.

Side effects antihistamines include anticholinergic effects such as drowsiness, dry mouth, blurry vision, constipation, difficulty urinating, disorientation, and dizziness (especially when standing up). Prescription antihistamines often have fewer of these side effects.

Some antihistamines are more likely to cause drowsiness (sedation) than others. Antihistamines that cause drowsiness are widely available over the counter. Patients should not take these antihistamines if they intend to drive vehicles. means, work with heavy equipment or engage in other activities that require vigilance. Antihistamines that cause drowsiness should not be given to children under 2 years of age because they can have serious or life-threatening side effects. Also because of their anticholinergic effects, these antihistamines pose a particular problem for the elderly and for people with glaucoma, benign prostatic hyperplasia, constipation, or dementia. In general, doctors are wary of prescribing antihistamines for patients with cardiovascular disease.

Everyone responds differently to antihistamines. For example, natives of Asia are less susceptible to the sedative effect of diphenhydramine than Europeans. Also, in some people, antihistamines cause the opposite (paradoxical) reaction; such people become nervous, restless and agitated.

- Mast cell stabilizers.

Mast cell stabilizers block the release of histamine and other substances that cause swelling and inflammation by mast cells.

Mast cell stabilizers are indicated when antihistamines and other drugs are ineffective or have unpleasant side effects. These medications can help control allergy symptoms.

These include azelastine, cromolyn, lodoxamide, ketotifen, nedocromil, olopatadine, and pemirolast. Azelastine, ketotifen, olopatadine, and pemirolast are also antihistamines.

Cromoline available by prescription:

• for use with inhaler or nebulizer (to deliver the drug in the form of an aerosol to the lungs);
• in the form of eye drops;
• in dosage forms for oral administration.

As a nasal spray, cromolyn is available without a prescription for treatment allergic rhinitis. Cromoline usually affects only the areas where it is applied, such as the back of the throat, the lungs, the eyes, or the nasopharynx. When taken orally, cromolyn may relieve the digestive symptoms of mastocytosis, but it is not absorbed into the bloodstream and thus has no effect on other allergy symptoms.

- Corticosteroids.

When allergy symptoms cannot be controlled with antihistamines and mast cell stabilizers, corticosteroids may help.

Corticosteroids can be used as a nasal spray to treat nasal symptoms or via an inhaler, usually to treat asthma.

Doctors give corticosteroids (such as prednisone) by mouth only when symptoms are severe or severe and all other treatments have failed. When taken by mouth in high doses and over a long period (eg, more than 3–4 weeks), corticosteroids can cause many side effects, sometimes severe. Therefore, oral corticosteroids are prescribed for the shortest possible time.

Creams and ointments containing corticosteroids can help relieve itching caused by an allergic rash. One of the corticosteroids, hydrocortisone, is available without a prescription.

- Other drugs.

Leukotriene modifiersfor example, montelukast are anti-inflammatory drugs used to treat the following conditions:

• mild persistent asthma;
• allergic rhinitis.

They inhibit leukotrienes secreted by some leukocytes and mast cells when exposed to allergens. Leukotrienes promote inflammation and constrict the airways.

Omalizumab - a monoclonal antibody (an artificial [synthetic] antibody designed to interact with a specific substance). Omalizumab binds to immunoglobulin E (IgE), antibodies produced in large quantities during allergic reaction, and prevents IgE from binding to mast cells and basophils, preventing allergic reactions. Omalizumab can be used to treat persistent or severe asthma when other treatments have failed. With frequent relapses of urticaria and the lack of effect from other methods of treatment, its appointment may be advisable. With omalizumab, the dose of corticosteroids can be reduced. Omalizumab is used by injection under the skin (s / c).

- Emergency treatment.

Severe allergic reactions, such as anaphylactic reaction, require urgent treatment.

People who have severe allergic reactions should always carry a pen with a epinephrinewhich should be used as soon as possible if a serious reaction occurs. Antihistamine tablets can also help, but epinephrine must be given before taking them. Usually, epinephrine stops the reaction, at least temporarily. However, a person who has had a severe allergic reaction should go to the ward emergency care under the supervision of doctors, where treatment can be repeated or changed as necessity.

- Treatment of allergies during pregnancy and breastfeeding.

Pregnant women with allergies should avoid allergens whenever possible to control their symptoms. If symptoms are severe, pregnant women should use an antihistamine nasal spray. They may only take oral antihistamines if the antihistamine nasal spray does not help.

Women who are breastfeeding should also avoid taking antihistamines. But if antihistamines are needed, doctors prefer to use antihistamines, which are less likely to cause drowsiness, and they prefer antihistamines nasal sprays over drugs for oral administration application. If oral antihistamines are needed to control symptoms, they should be taken immediately after feeding the baby.

Prophylaxis

- Environmental factors.

It is best to avoid or eliminate the allergen whenever possible. Measures to prevent exposure to the allergen may include the following:

• discontinuation of the drug;
• keeping a pet outside the home or limiting its stay to certain premises;
• use of high-efficiency particulate air (HEPA) filters and vacuum cleaners;
• refusal from certain foods;
• for people with severe seasonal allergies, it is possible to move to an area without these allergens;
• removing or replacing items that collect dust, such as upholstered furniture, carpets and souvenirs;
• the use of mattress toppers and pillowcases made of thin fabric, through which dust and particles of allergens cannot penetrate;
• use of synthetic fiber pillows;
• Frequent washing of sheets, pillowcases and blankets in hot water;
• regular cleaning of the house, including dusting, vacuuming and wet cleaning;
• the use of air conditioners and dehumidifiers in basements and other damp rooms;
• steam treatment at home;
• destruction of cockroaches.

People with allergies should avoid or minimize exposure to certain other irritants that can aggravate allergy symptoms or cause breathing problems. Such irritants include the following:

• tobacco smoke;
• strong odors;
• irritating vapors;
• air pollution;
• cold temperature;
• high humidity.

- Allergen immunotherapy (desensitization).

If it is impossible to avoid certain allergens, especially airborne ones, as well as the ineffectiveness of drugs for the treatment of allergic reactions, allergen-specific immunotherapy can be used, usually in the form of injections (injections), to reduce the sensitivity of patients to this allergen.

Allergen-specific immunotherapy can prevent allergic reactions or reduce their number and / or severity. However, allergen immunotherapy is not always effective. Some people and some allergies respond better than others.

Immunotherapy is most commonly used to treat allergies to the following irritants:

• pollen;
• house dust mites;
• mold fungi.
• poison from the sting of insects.

Immunotherapy helps prevent anaphylactic reactions when you are allergic to allergens that cannot be avoided, such as insect venom. It is sometimes used to treat animal hair allergies, but this treatment is unlikely to be effective. Immunotherapy studies for food allergies are ongoing.

Immunotherapy is not used if it is possible to avoid contact with an allergen, such as penicillin and other medications. However, if patients must take a medication to which they are allergic, immunotherapy under the supervision of a physician may be given to desensitize them.

During immunotherapy, a small amount of the allergen is injected under the skin. The dose is gradually increased until a dose sufficient to control symptoms is reached (maintenance dose). The increase must necessarily be gradual, since too rapid exposure to a high dose of the allergen can cause an allergic reaction. Injections are usually given once or twice a week until a maintenance dose is reached. Then the injections are done once every 2-4 weeks. For optimal effectiveness, maintenance injections should be continued throughout the year, even to combat seasonal allergies.

Alternatively, high doses of the allergen can be placed under the tongue (sublingually), held there for a few minutes, and then swallowed. As with injections, the dose is gradually increased. The sublingual route is relatively new, so the frequency of dosing of the allergen has not been established. It varies from once a day to 3 times a week. To prevent allergic rhinitis, extracts from herb pollen or house dust mites can be placed under the tongue.

Allergen-specific immunotherapy can last 3-4 years.

Because injections used during immunotherapy sometimes cause dangerous allergic reactions, patients should remain in the doctor's office for at least 30 minutes after the procedure. In cases of mild reactions to immunotherapy (eg, sneezing, coughing, fever, tingling sensation, itching, tightness in the chest, wheezing, and hives) may be helped by taking medications, usually antihistamines such as diphenhydramine or loratadine. For more severe reactions, epinephrine (adrenaline) is administered.