From mild seasonal allergies to severe anaphylactic allergic reactions, most people have experienced some type of allergy in their life, but why are some so severe and some so mild? An allergic reaction in essence is the bodies overreaction to something not harmful being identified as a harmful. Allergies develop in two phases: sensitization and re-exposure. During sensitization, the body is experiencing the initial exposure, much like a vaccine. Specifically, dendritic cells are identifying the allergen. These dendritic cells then activate T-helper cells, which then signal the B-cells. The B-cells then produce IgE (immunoglobulin-E) antibodies for the given allergen which bind to mast cells. An IgE is not a type of cell, but rather a type of antibody. Through the entirety of this process, there is no presentation of symptoms yet. Symptoms begin to present during re-exposure when the allergen binds to the IgE cells created during the sensitization phase. Once the allergen is bound to the IgE cells, inflammatory chemicals such as histamines are introduced to the body. The overload of histamine is ultimately what creates the symptoms of an allergy. The difference between a mild allergy and anaphylaxis is the scale on which these inflammatory chemicals are distributed through the body. In a mild reaction, the release will be localized to one area of the body, while in an anaphylactic reaction, the release is widespread across the entire body. When inflammatory chemicals such as histamines flood the entire body so quickly, there are physiological effects that cause the classic symptoms of anaphylaxis such as vasodilation, increased vascular permeability, and smooth muscle constriction. Anaphylaxis is a life threatening condition, but can be counteracted by administering epinephrine. Epi is effective at treating anaphylaxis because it has the exact opposite effect on the body of inflammatory chemicals. Epinephrine constricts blood vessels, relaxes smooth muscles, and stabilizes mast cells to slow the release of inflammatory chemicals causing the reactions. There are many different types of allergic reactions, and just about anything can be an allergen to someone based on their genetics, environment, or microbiome to name a few. The underlying cause of an allergy can't be attributed to just one thing, but rather a multitude of different things all impact what one may be allergic to, and how severe that allergy is.
American Academy of Allergy Asthma and Immunology. (2021). Allergic Reaction | AAAAI. Aaaai.org. https://www.aaaai.org/Tools-for-the-Public/Conditions-Library/Allergies/Allergic-Reactions
Chipps, B. (2022, August 31). What Is Epinephrine? | Allergy & Asthma Network. Allergy & Asthma Network. https://allergyasthmanetwork.org/anaphylaxis/what-is-epinephrine/
Janeway, C. A., Travers, P., Walport, M., & Shlomchik, M. J. (2012). Effector mechanisms in allergic reactions. Nih.gov; Garland Science. https://www.ncbi.nlm.nih.gov/books/NBK27112/
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