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Allergy
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An allergy is an exaggerated reaction of the immune system to something that is harmless to almost everyone: pollen, a food, pet dander or fur. The technical name for that mechanism is type I hypersensitivity.
The first time the body meets that substance, the allergen, it becomes sensitized. It makes an antibody called immunoglobulin E, a defense protein built to fit that allergen, and leaves it anchored to the surface of two cell types, the mast cell and the basophil, which are defense cells loaded with granules. The next time the allergen comes in, it bridges two antibodies already anchored to the cell, and that bridge is the order to fire.
The cell then degranulates, meaning it opens its granules all at once and releases histamine, leukotrienes and prostaglandins, substances that inflame the tissue where they land. Depending on where this happens, it shows up as welts on the skin, which is urticaria; as a stuffy nose and sneezing, which is allergic rhinitis; as asthma; as an allergy to a food; or as angioedema, the deep swelling of the lips or eyelids.
In brief
Allergy is a type I hypersensitivity, an immunoglobulin E-mediated response to normally harmless environmental antigens.
During sensitization the body makes specific immunoglobulin E that binds to receptors on mast cells and basophils; on re-exposure the allergen cross-links it and the cell degranulates.
The allergen bridges two antibodies on the cell: that bridge is the order to fire.
Degranulation releases histamine, leukotrienes and prostaglandins, and that cascade produces conditions such as urticaria, allergic rhinitis, asthma, food allergy and angioedema.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingType I Hypersensitivity Reaction, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated