Allergies are an abnormal response by the immune system to substances that usually do not cause damage. This erroneous defence mechanism produces an inflammatory process that can affect any part of the allergy sufferer's body, causing a large variety of diseases: rhinitis, conjunctivitis, bronchial asthma, hives, dermatitis, anaphylaxis... Allergic diseases have a hereditary component and an environmental influence.

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alergologiaalergologiaTypes of allergies

Types of allergies

The body can overreact due to countless agents, which are called allergens.

Depending on the type of allergen

The most common allergies can be classified according to the type of allergen:

    • Food allergies

      Milk, eggs, dried fruit and nuts and wheat are some food products that can produce allergies.

      In general, allergic reactions affect the digestive system (vomiting, diarrhoea, nausea, etc.) but can also cause skin issues (such as hives) or affect the cardiovascular system or respiratory system (rhinitis, asthma, etc.).

      It is common for food allergies to be confused with intolerances, which are very different; in the case of intolerances, the body is not able to metabolise a certain nutrient because it lacks the necessary catalyst.

    • Drug allergies

      Any drug can cause an allergy, although some statistically have greater incidence. Symptoms can vary from skin rashes, fever and serious diseases of several vital systems that can put the person's life at risk (anaphylaxis).

      Drug allergies should not be confused with side effects or the effects an overdose of a certain drug may produce.

      Symptoms generally appear immediately, although sometimes they may appear after a few days or even weeks.

    • Insect allergies

      Most allergies of this kind appear due to being bitten by a few Hymenoptera insects: wasps, bees and some ant species.

      It is normal for the autoimmune system to react against insect venom and that redness and swelling appear in a localised manner, but when someone is allergic, symptoms can be much more severe: palpitations, respiratory distress, dizziness and even anaphylaxis.

Depending on the allergy symptoms

Depending on the allergy symptoms, they can be classified in the following categories:

    • Skin allergies

      Cutaneous diseases due to allergies are very common regardless of the allergen that produces them. Among these, the following are noteworthy:
      • Atopic dermatitis.- It is marked by the inflammation and reddening of the skin, with desquamation, itchiness, dryness, etc.

      • Allergic contact dermatitis.- Symptoms are similar to atopic dermatitis but the difference lies in that contact dermatitis appears when in direct contact with the allergen. Agents that produce these symptoms are as varied as plants, metals, soaps, fragrances, etc.

      • Hives.- This is an oedematous skin lesion (colloquially wheals) that causes itchiness.

      • Angioedema: Fluid accumulates in the interstitial spaces (between cells) in the skin and mucosae. Instead of swelling appearing superficially as in the case of hives, it appears under the skin.

    • Allergic conjunctivitis

      Conjunctivitis is an inflation of the "conjunctiva", a mucous membrane that covers the anterior area of the eye and the inside of the eyelids. The eyes will be red, watering, itchy and stinging.

    • Allergic rhinitis

      LThe mucosae in the nasal cavities are inflamed, producing abundant secretions and itchiness, accompanied by frequent sneezing and loss of sense of smell.
      Depending on the allergen, rhinitis can be seasonal (hay fever, an allergy to pollen that only appears during some seasons, is very common), temporary or perennial (caused, for example, by dust or mites).

    • Allergic asthma

      Asthma is a bronchial inflammatory disease. Typical symptoms include coughing, shortness of breath, wheezing and tightness in the chest. Allergic or extrinsic asthma appears when the person is in contact with the allergen they are sensitive to. They can experience crisis caused directly by physical exercise, respiratory infections or non-specific irritants.
alergologiaalergologiaDiagnostic tests

Diagnostic tests

To diagnose the agent causing an allergy and depending on the symptoms that appear, a series of tests may be carried out:

    • Cutaneous tests

      These tests are very safe and would only cause complications with patients who are highly sensitive to an allergen. In case of any issues, the allergist will be duly prepared with the necessary treatment.

      • Prick test.- This is the most frequently used technique, consisting of placing drops with different potential allergen extracts on the skin and making small punctures on the spots where they have been placed. In around 15 minutes, we will be able to tell if there has been a notable reaction to any of the agents tested.

      • Patch test: Instead of punctures, a number of patches are placed on the patient's back containing the concentrated agents to be studied. After 48 hours, the patient must return to the doctor's office to assess the reactions.

    • Laboratory tests

      A small amount of blood is extracted from the patient and sent to the laboratory. The laboratory will study allergen-specific E immunoglobulin (IgE), which will show the concentration of antibodies (produced by the immune system). A high concentration of certain antibodies may indicate the body has overreacted to an allergen, that is, an allergy.
      Laboratory tests are used to detect allergies to certain drugs, food, dust mites, animal dander, etc.

    • Respiratory function tests

      • Spirometry: It consists of measuring the amount of air that is forcefully inspired and expired and how long it takes. This procedure is repeated at least three times and the values are compared with reference values according to the patient's age, weight, height and sex. This test allows us to measure pulmonary function and, for example, can help to diagnose bronchial asthma or perform a check-up.

      • Bronchodilator test: This test includes performing a spirometry, then inhaling a bronchodilator to then repeat the spirometry after 15 minutes. When comparing the values, if an improvement of more than 12% is observed in the spirometry after inhaling the bronchodilator, we can confirm bronchial asthma that may be caused by an allergy.

      • Peak-flow measurement:

        Peak-flow is the maximum speed a person can breathe at.

        The meter is a small portable device that will help the asthmatic patient to control the respiratory condition they are in before symptoms appear and, for example, inhale the bronchodilator accordingly.

        This test cannot substitute a spirometry.

      • Oxygen saturation:

        The amount of oxygen available in the blood provides cells with the fuel necessary for their metabolic functions. We have seen that some allergies affect the respiratory system, which means that blood oxygen saturation will be poor.

        Saturation below 90% is considered hypoxaemia and the patient will have difficulty breathing and will become exhausted with little effort. When saturation falls below 80%, hypoxaemia is severe and respiratory issues are great.

        To measure saturation, we use a pulse oximeter that emits light at different frequencies. The pulse oximeter is usually placed against a fingertip (a more or less translucent area of the body) and is able to "read" the colour of arterial blood. The clearer and brighter the colour of the blood, the more oxygen saturation.

        Another means for measuring saturation is through arterial blood gases.

Exposure tests

    To see the degree to which a patient is sensitive to a specific allergen, they can be exposed to it in a controlled setting. Several exposure pathways are used:
    • Respiratory.- Effects are observed when the allergen is breathed in. The effects can be observed both in the nose and the bronchi.
    • Oral: It is usually used to observe the effect of a food or drug product.
    • Conjunctival: The allergen is mixed with eye drops and the effects are observed on the eye.
alergologiaalergologiaSpecific treatments

Specific treatments

To fight allergies, we have access to a range of treatments that require prior assessment to consider their suitability.

  • Immunotherapy: Allergenic vaccinations

    The patient is administered the allergenic component in very small doses which are increased as the treatment progresses to gradually induce tolerance by the autoimmune system.

    Immunotherapy is indicated for allergies where avoiding exposure to the allergen is not possible: dust mites, pollen, etc. As well as those caused by animal dander, latex or some food allergies like peach.

    Administration can be sublingual or subcutaneous.

  • Induction to food tolerance

    This treatment is used mainly in children who are allergic to eggs and milk. Just as in the case of vaccinations, minimum doses are administered orally and subsequent doses are increased.
    The first dose is usually administered at the hospital, where the child is monitored, and then the dose is repeated at home. The process will be repeated by increasing the doses, first at the hospital and then at home.

  • Drug desensitisation

    This treatment is usually applied when there is no alternative to the drug that causes the allergy. The most common drugs that we try to desensitise patients to are anticancer drugs (taxanes, platinums, etc.) and antibiotics, although in this case they can often be replaced by sulphonamides.

    The procedure also begins by administering minimal doses which are gradually increased. The goal is to achieve tolerance to the therapeutic dose indicated for the pathology that this drug is for.