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Inhaled or ingested allergens usually cause immediate hypersensitivity reactions.
Delayed hypersensitivity reactions, also known as type IV hypersensitivity reactions, are caused by T cells recognizing antigens and triggering an immune response. This can happen hours to days after exposure to the antigen. Common triggers include certain drugs, metals, and infectious agents.
Hypersensitivity (also called hypersensitivity reaction) refers to undesirable reactions produced by the normal immune system, including allergies and autoimmunity. These reactions may be damaging, uncomfortable, or occasionally fatal. Hypersensitivity reactions require a pre-sensitized (immune) state of the host. The four-group classification was expounded by P. H. G. Gell and Robin Coombs in 1963. (Wikipedia)
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Delayed hypersensitivity reactions-- Allergic reactions mediated by T cells that occur hours to days after exposure
Delayed hypersensitivity reactions are immune responses that occur several hours to days after exposure to an antigen. They are mediated by T cells rather than antibodies, leading to the release of inflammatory mediators and recruitment of immune cells to the site of antigen exposure. Examples include contact dermatitis, tuberculin skin tests, and some drug reactions.
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The most common type of immediate hypersensitivity is type I hypersensitivity, also known as allergic reactions. This type of hypersensitivity involves the production of IgE antibodies in response to an allergen, which leads to the release of histamine and other mediators that cause symptoms such as itching, hives, and anaphylaxis.
An atopy is a hereditary disorder marked by the tendency to develop localized immediate hypersensitivity reactions to allergens.
The medical term for a substance that produces hypersensitivity is an allergen. Allergens can trigger allergic reactions in individuals who are sensitive to them, leading to symptoms such as sneezing, itching, and hives.
Mariana C. Castells has written: 'Anaphylaxis and hypersensitivity reactions' -- subject(s): Hypersensitivity, Anaphylaxis, Acute phase reaction, Clinical immunology, Allergy, Acute-Phase Reaction
Hypersensitivity reactions should be considered with organic compounds such as chlorhexidine, benzalkonium and hexachlorophine.