Understanding Allergy: Symptoms, Causes, Diagnosis, Management

Definition of allergy and exaggerated immune response

An allergy is defined as an exaggerated immune response in which the body mistakenly treats an ordinarily harmless substance (an allergen) as a threat. This misidentification leads to allergic reactions and allergic diseases such as hay fever (allergic rhinitis), allergic conjunctivitis, allergic asthma, atopic dermatitis, food allergies, and anaphylaxis. Allergic reactions occur when allergens interact with the immune system—commonly involving IgE antibodies that bind to allergens and then to receptors on mast cells or basophils, triggering the release of inflammatory chemicals such as histamine. As a result, symptoms can affect multiple body systems, including the skin (itchy rash, hives), airways (sneezing, coughing, wheezing, shortness of breath), and the gut (vomiting, diarrhea, abdominal discomfort).

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Common symptoms by affected organ systems

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