An allergy is an excessive response by the immune system to substances that are usually harmless to most people, such as pollen, dust or certain foods. When these substances, called allergens, come into contact with the body, the latter perceives them as a threat, triggering a reaction that can cause symptoms such as skin rashes, sneezing or breathing difficulties. Allergies can vary in severity, from mild irritation to life-threatening reactions such as anaphylactic shock.
Definition and meaning
Allergies can be classified into several types, depending on the allergen involved and how exposure occurs. For example, food allergies result from the consumption of certain foods, while environmental allergies are caused by exposure to substances present in the environment, such as pollen or dust mites. Diagnosis of allergies may include skin tests or blood tests to identify the specific allergens responsible for reactions.
Allergy treatment varies according to the severity and type of allergy. It may include allergen avoidance, the use of antihistamines, steroids or other forms of anti-inflammatory medication, and in some cases, allergen immunotherapy, which aims to gradually desensitize the immune system to the allergen.
Evaluation
Allergy assessment is an essential process for identifying the specific allergens responsible for allergic reactions in an individual. Here are the key steps in allergy assessment:
- Detailed medical history: The physician begins by taking a full history of the patient's symptoms, including their nature, duration and context of onset. He also looks at the patient's family history of allergies, environmental conditions and diet.
- Physical examination: A physical examination can detect physical signs of allergy, such as skin rashes, edema or respiratory problems.
- Skin tests (prick tests): Skin tests are often used to identify allergies to pollens, dust mites, animal hair and molds. A small amount of the suspected allergen is applied to the patient's skin, usually on the forearm or back, and the skin is lightly pricked to allow the allergen to penetrate. A positive reaction, usually a small, red, itchy elevation, indicates allergy to that allergen.
- Blood tests (specific IgE assays): Blood tests measure the levels of specific IgE antibodies to certain allergens in the blood. These tests are useful when skin testing is not possible, for example in patients taking certain medications or those with extensive skin conditions.
- Provocation tests: These tests, carried out under strict medical supervision, involve progressive exposure of the patient to the allergen in order to observe the reaction. They are often used for food or drug allergies when other tests are inconclusive.
- Elimination and reintroduction test: Mainly used for food allergies, this test involves eliminating suspect foods from the patient's diet, followed by reintroducing them one by one to observe reactions.
These tests not only confirm the presence of allergies, but also guide management and treatment by identifying specific allergens to which the patient should avoid exposure.
Causes of allergic reactions
Allergic reactions occur when the immune system overreacts to normally harmless substances in the environment. Here is a summary of the main causes identified by scientific research:
- Drug reactions: Some allergic reactions are caused by a specific immunological response to drugs, which may release allergic mediators non-immunologically, inducing symptoms ranging from urticaria to more severe reactions such as anaphylaxis (Parker, C. (1982). Allergic reactions in man. Pharmacological reviews, 34 1, 85-104).
- Food allergies: Specific proteins in foods such as peanuts, cow's milk and seafood can cause severe allergic reactions, including anaphylaxis. These reactions can also be exacerbated by factors such as advanced age or the presence of asthma (Flinn, A., & Hourihane, J. (2013). Allergic Reaction to Peanuts: Can We Predict Reaction Severity in the Wild?”. Current Allergy and Asthma Reports, 13, 645-650. https://doi.org/10.1007/s11882-013-0369-5.).
- Allergen inhalation: Inhalation of food particles or other environmental allergens can lead to severe respiratory symptoms, including asthma and anaphylaxis (James, J., & Crespo, J. (2007). Allergic reactions to foods by inhalation. Current Allergy and Asthma Reports, 7, 167-174. https://doi.org/10.1007/S11882-007-0017-Z.).
- Exposure to environmental allergens: Allergens such as pollens, dust mites and molds can trigger allergic reactions in sensitized individuals. These reactions are often mediated by immunoglobulin E (IgE) which, when activated, releases chemical mediators causing immediate symptoms (Averbeck, M., Gebhardt, C., Emmrich, F., Treudler, R., & Simon, J. (2007). Immunologic Principles of Allergic Disease. JDDG: Journal der Deutschen Dermatologischen Gesellschaft, 5. https://doi.org/10.1111/j.1610-0387.2007.06538.x.).
Summary
Allergic reactions are mainly caused by an excessive immune response to normally harmless environmental, drug or food substances. Understanding the specific triggers can help to better manage and prevent these reactions.
Intolerance, Allergy or Anaphylaxis?
Allergy
An allergy is a reaction of the immune system to a foreign substance, which is generally not harmful to most people. These substances, called allergens, can include pollen, certain foods and dust, among others. Allergy occurs when the immune system overreacts to these allergens, producing IgE antibodies. These antibodies trigger the release of chemicals such as histamine by immune cells, leading to allergic symptoms such as itching, skin rashes, breathing difficulties and edema.
Intolerance
Unlike allergy, intolerance does not involve the immune system. It's a case of difficulty in digesting certain substances, often due to an enzyme deficiency. For example, lactose intolerance is caused by a deficiency in lactase, the enzyme needed to break down the lactose found in dairy products. Symptoms of intolerance are generally gastrointestinal, such as bloating, abdominal pain and diarrhea, and do not threaten the immune system or provoke acute inflammatory reactions.
Anaphylaxis
Anaphylaxis is a severe, rapid and potentially fatal allergic reaction. It is considered to be the most extreme expression of an allergic reaction, and can be triggered by food allergens, insect stings, drugs and more. Anaphylaxis causes a massive release of chemicals by the immune system, which can lead to severe shock and a drop in blood pressure. Symptoms can include difficulty breathing, a generalized rash, a feeling of impending discomfort, and loss of consciousness. Anaphylaxis requires urgent medical intervention, often in the form of epinephrine injections.
Summary
The main distinction between an allergy and an intolerance lies in the involvement of the immune system in the case of allergies, unlike intolerances which are linked to digestive problems. Anaphylaxis, on the other hand, is a serious and urgent form of allergy requiring immediate medical attention. These distinctions are crucial to the proper diagnosis and treatment of symptoms.
Treatment
Treatment of allergies depends on their type and severity. Here are several strategies commonly used to manage and treat allergic reactions:
- Avoid allergens: The first step in treating allergies is to avoid known allergens. This may mean staying indoors on high pollen days, using dust mite covers for bedding, or avoiding certain foods or medications.
- Medications :
- Antihistamines: These medications help reduce itching, sneezing, and other symptoms caused by the release of histamine.
- Decongestants: These are useful for relieving nasal and sinus congestion.
- Nasal steroids: These sprays help reduce inflammation in the nasal passages.
- Mast cell stabilizers: These agents prevent the release of histamine and are often used to prevent allergy symptoms.
- Immunotherapy: Also known as desensitization, this method treats the underlying causes of allergies. It involves the regular administration of increasing doses of allergens, allowing the body to gradually acclimatize and reduce its reaction to these substances.
- Biological treatments: For severe cases, such as allergic asthma or atopic dermatitis, biological drugs targeting specific immune pathways can be used.
- Self-injectable epinephrine: For those at risk of severe allergic reactions, such as anaphylaxis, carrying an epinephrine auto-injector is essential. This enables rapid administration of medication in an emergency.
- Education and action plan: It's crucial for allergy sufferers and those around them to know the signs of an allergic reaction and how to act in an emergency. This includes training in the use of medication and recognizing symptoms that require immediate intervention.
Allergy management can involve a combination of these strategies, tailored to the specificity and severity of each individual's allergy.
In brief
Allergies are reactions of the immune system to substances that are harmless to most people, such as pollen, dust or certain foods. Exposure to these allergens provokes an excessive immune response, where the body perceives them as a threat, triggering symptoms such as skin rashes, sneezing or breathing difficulties. Allergies can vary in severity, from mild irritation to life-threatening reactions such as anaphylactic shock. Allergy diagnostics may include skin tests or blood tests to identify the specific allergens responsible. Treatment may involve allergen avoidance, medications such as antihistamines or steroids, and in some cases, allergen immunotherapy to desensitize the immune system.
Sources
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- J. Larsen, L. Broge, H. Jacobi : 2016 « Allergy immunotherapy: the future of allergy treatment. » https://doi.org/10.1016/j.drudis.2015.07.010 [Last consulted May 8, 2024]
- F. Blanco-Pérez, G. Papp, A. Goretzki, Tobias-Maximilian Möller, Martina Anzaghe, S. Schülke : 2019 « Adjuvant Allergen Fusion Proteins as Novel Tools for the Treatment of Type I Allergies. » https://doi.org/10.1007/s00005-019-00551-8 [Last consulted May 8, 2024]