Definition of allergy and exaggerated immune response

Summary

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).

Key Points

• 1

  Allergy is an exaggerated immune response to an allergen that is usually harmless to most people.

• 2

  Allergic reactions commonly involve IgE antibodies activating mast cells/basophils, leading to release of inflammatory mediators like histamine.

• 3

  Allergies can produce symptoms across multiple organs, including skin, airways, and the gastrointestinal tract, and may range from mild reactions to anaphylaxis.