An allergic reaction is the response of the human immune system to contact with an allergen. Symptoms of an allergic reaction most often appear on the skin and mucous membranes, in the digestive tract and in the respiratory tract. Find out what factors can trigger allergic reactions and how to diagnose and treat them. How do allergic reactions arise? What are their types?

An allergic reactionis the result of the stimulation of the immune system caused by a specific substance. The factor that causes an allergic reaction is called an allergen.An allergic reactionmay be violent or chronic. Diseases arising from an allergic reaction include bronchial asthma, atopic dermatitis, allergic rhinitis, and food allergies.

Allergic reaction - how does it arise?

The ingress of an allergen into the human body causes it to be recognized and "remembered" by the cells of the immune system. This is called allergic phase of an allergic reaction. Then, antibodies against the allergen are formed in the blood.

Each subsequent contact with an allergen may stimulate the reaction of the immune system. This is when the allergy phase occurs. Although the allergen does not pose a great threat to the body, the immune system is highly hypersensitive to it. An allergic reaction occurs which, depending on the type of allergen and the individual susceptibility of the organism, may have different localization, character and intensity.

The purpose of an allergic reaction is to eliminate the allergen through the cells of the immune system. This immune response causes a number of symptoms, collectively known as allergies.

Allergic reaction - types

An allergic reaction is a very complex phenomenon, hence the wide variety of symptoms. An allergic reaction can be caused by 4 different mechanisms of allergy development. The explanation of these mechanisms was developed in the 1960s in the so-called the Gell-Coombs classification. This classification is still used today in describing allergic reactions.

Type I allergic reaction

The most commonly known type of allergic reaction is calledimmediate reaction, also known as Type Iallergy. Allergic reactiontype I is responsible for the most common allergic diseases:

  • allergic rhinitis,
  • anaphylaxis,
  • bronchial asthma.

It is based on IgE class antibodies directed against various allergens. The other types of allergic reactions are somewhat less known.

Type II allergic reaction

Wthe type II reactioninvolves IgM and IgG antibodies and damages cells recognized by the immune system as foreign. An example of a type II allergic reaction is a serological conflict in the fetus, in which its blood cells are destroyed by antibodies produced in the mother's body.

Type III allergic reaction

WType III reactionstake part in the so-called immune complexes. They are combinations of antigens with antibodies that accumulate in various organs (kidneys, skin, blood vessels). Type III allergic reaction is at the root of many inflammatory diseases, including rheumatoid arthritis and systemic lupus erythematosus.

Type IV allergic reaction

Type IV allergic reactionis the so-called delayed type hypersensitivity. Unlike other types of allergies, a type IV reaction occurs some time after contact with the allergen (usually a minimum of 72 hours).

The main cells involved in this type of allergic reaction are T cells. An example of a type IV allergy disease is allergic contact dermatitis.

Allergic reaction - symptoms

The essence of an allergic reaction is inflammation resulting from the stimulation of the immune system. Symptoms of an allergic reaction vary in severity. In many cases, an allergic reaction develops in an organ that is in direct contact with the allergen. We are talking then about an organ-specific allergic reaction.

In the case of inhaled allergens (e.g. grass pollen), symptoms mainly affect the conjunctiva, the nasal mucosa and the respiratory tract. On the other hand, food allergens can cause gastrointestinal symptoms (flatulence, diarrhea).

We must remember, however, that the human immune system is an integral whole. If an allergen stimulates a specific group of immune cells, it may cause an allergic reaction, the effects of which will be visible in a seemingly distant organ (for example - eczema on the skin after eating an allergenic food).

Anaphylaxisis an example of the most severe, generalized allergic reaction. In the course of anaphylaxis, allergy symptoms develop rapidly and affect many organs simultaneously.The most serious form of anaphylaxis is anaphylactic shock, which causes a sudden drop in blood pressure.

The most effective treatment for anaphylactic shock is immediate intramuscular injection of adrenaline. People prone to severe allergic reactions usually carry a dose of this drug with them. The incidence of diseases related to allergic reactions is systematically increasing.

Allergy symptoms most often concern three systems

Symptoms of allergic reactions in most cases concern three organs (systems) in the human body:

  • airways,
  • digestive system
  • and skins.

Sensitization to airborne allergens most often causes allergic rhinitis, allergic conjunctivitis or bronchial asthma.

Allergic rhinitis manifests itself:

  • chronic runny nose,
  • sneezing
  • and a reflex cough.
  • In the presence of conjunctivitis, redness, itching and tearing appear.

The main symptom of bronchial asthma is:

  • shortness of breath
  • and bronchospasm caused by inhalation of a specific allergen.

The symptoms of food allergies are:

  • stomach pains,
  • diarrhea
  • and indigestion after eating allergic foods.

In young children, food allergies can inhibit physical development . Allergic reactions also cause various types of dermatological diseases. An immediate allergic reaction in the skin causes hives, in the course of which characteristic blisters appear.

An example of achronic allergic skin diseaseis atopic dermatitis. There are several mechanisms of allergic reactions at the root of this condition. The main symptoms of AD are:

  • chronic itching of the skin,
  • damage to the epidermal barrier,
  • eczema
  • and extreme dryness of the skin requiring intensive care.

Allergic reaction - triggers

The factors that trigger an allergic reaction are called allergens. Substances that trigger an allergic reaction can enter the body through various routes. On this basis, the following are distinguished:

  • inhaled allergens,
  • food,
  • and contact.

Inhaled allergens

Inhaled allergensmay cause seasonal or year-round allergic reactions. The most common seasonal allergens are:

  • pollenplants (grasses, trees),
  • and fungal spores.

Year-round inhalation allergens include :

  • mites occurring in the home environment,
  • mold
  • and animal allergens (including cat hair).

Food allergens

Food allergensare a huge group of substances that cause unwanted allergic reactions when ingested. The most common food allergens are:

  • cow's milk protein,
  • eggs,
  • peanuts,
  • shellfish and seafood,
  • citrus,
  • soybeans
  • and cereal proteins.

Contact allergens

Contact allergensis a group of substances responsible for e.g. for allergic contact dermatitis. Skin changes occur where these substances come into direct contact with the skin. The most common contact allergens are:

  • latex (e.g. in protective gloves),
  • chrome and nickel (found in jewelry and parts of clothing - belts, buttons),
  • as well as numerous substances included in cosmetics.

People prone to contact allergic reactions should always pay attention to the composition of skin care products.

Drugs

A separate group of substances causing allergic reactions aredrugs . Adverse allergic reactions following the use of drugs may be local (rash, dyspnoea, diarrhea) and generalized (anaphylaxis).

Confirmed allergy to a specific drug is an absolute contraindication to the use of this preparation, as well as other drugs belonging to the same group.

Among all medications, allergic reactions most often occur after beta-lactam antibiotics, which include, among others, penicillins.

Other groups of drugs that often cause allergic reactions include salicylate derivatives (aspirin), contrast agents used in radiological examinations, and anesthetics.

Allergic reaction - diagnosis

Symptoms of allergic reactions are an indication for a diagnosis that will help determine the factor causing the reaction, and implement appropriate treatment. The medical history is the basis for the diagnosis of all allergic diseases. In many cases, patients are able to observe for themselves what triggered an allergic reaction.

Allergy tests are another diagnostic tool. Depending on the indications, the following is performed:

  • skin tests,
  • testing of specific IgE antibodies in the blood,
  • becontact allergy tests.

The results of these tests should always be interpreted in relation to the patient's symptoms. Particular care should be taken when testing for food allergies. Incorrect interpretation of the tests may lead to the unnecessary elimination of, for example, certain foods from the diet.

The presence of antibodies to certain food allergens in the blood is not yet evidence of an allergy. Many patients do not develop allergy symptoms despite being positive for the antibodies. For this reason, the removal of nutrients from the diet should take place only when consumption of a specific food causes repetitive side effects.

In the case of doubtful or contradictory test results, the so-called provocative attempts. Such attempts involve the administration of small amounts of substances that are suspected of causing an allergic reaction.

To increase the reliability of the test, the patient also receives a sample of the placebo substance. Provocation tests should be carried out under controlled conditions, in a place with adequate facilities to treat possible severe allergic reactions (anaphylaxis).

Allergic reaction - treatment

Prevention plays an important role in the treatment of allergic reactions. In the case of some factors responsible for causing allergic reactions, it is possible to avoid them (including most food and contact allergies, as well as drug allergies).

In the causal treatment of some allergic reactions, the so-called desensitization, technically known as Specific Allergen Immunotherapy. It is a type of therapy based on the administration of increasing doses of the sensitizing substance under controlled conditions.

Thanks to allergen immunotherapy, the patient's immune system is "switched over" and tolerance to a specific allergen develops. This method is only effective for certain allergens.

Allergen immunotherapy is a long-term process that requires regular medical visits to administer subsequent doses of the allergen. When an allergic reaction develops, medications are used to alleviate its course.

One of the important substances responsible for the symptoms of an allergic reaction is histamine. Antihistamines are the main group of agents used in the treatment of various allergic reactions. Currently, new generations of these drugs are available, free from troublesome side effects (e.g. excessive sleepiness).

Another group of medications reserved for the treatment of more severe reactionsallergies, there are glucocorticosteroids. The mechanism of action of these drugs enables the suppression of an excessive immune response.

Systemically administered glucocorticosteroids cause many side effects, therefore in the treatment of allergic reactions they are mainly used topically (intranasally, inhaled, and also in the form of an ointment on the skin).

Severe allergic diseases that do not respond to standard treatment may be an indication for the use of the so-called biological therapy. It is the newest type of therapy that targets specific components of the immune system that trigger allergic reactions.

An example of a drug used in biological allergy therapy is Omalizumab - a drug that affects IgE antibodies.

Finally, it is also worth mentioning adrenaline - a drug reserved for the treatment of the most violent, life-threatening allergic reactions. In the event of an anaphylactic shock, administering adrenaline is a life-saving procedure.

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Allergies