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Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis.
Hypersensitivity (also called hypersensitivity reaction or intolerance) is an abnormal physiological condition in which there is an undesirable and adverse immune response to antigen. [1] [2] It is an abnormality in the immune system that causes immune diseases including allergies and autoimmunity. It is caused by many types of particles and ...
Immunology. Type I hypersensitivity (or immediate hypersensitivity ), in the Gell and Coombs classification of allergic reactions, is an allergic reaction provoked by re-exposure to a specific type of antigen referred to as an allergen. [1] Type I is distinct from type II, type III and type IV hypersensitivities.
Types of allergens. Allergens can be found in a variety of sources, such as dust mite excretion, pollen, pet dander, or even royal jelly. [2] Food allergies are not as common as food sensitivity, but some foods such as peanuts (a legume ), nuts, seafood and shellfish are the cause of serious allergies in many people.
Oral allergy syndrome ( OAS) or pollen-food allergy syndrome (PFAS) is a type of allergy classified by a cluster of allergic reactions in the mouth and throat in response to eating certain (usually fresh) fruits, nuts, and vegetables. It typically develops in adults with hay fever. [1]
Type IV hypersensitivity, in the Gell and Coombs classification of allergic reactions, often called delayed-type hypersensitivity, is a type of hypersensitivity reaction that can take a day or more to develop. Unlike the other types, it is not humoral (not antibody-mediated) but rather is a type of cell-mediated response.
Allergy blood tests measure the presence of IgE antibodies to specific foods, pollens, mites, animals, insects and other environmental factors. (IgE, short for "immunoglobulin E", is the antibody that triggers food allergy symptoms.) The doctor looks at the test results to help determine if the patient has allergies.
Type II hypersensitivity, in the Gell and Coombs classification of allergic reactions, is an antibody mediated process in which IgG and IgM antibodies are directed against antigens on cells (such as circulating red blood cells) or extracellular material (such as basement membrane).
Allergic inflammation is an important pathophysiological feature of several disabilities or medical conditions including allergic asthma, atopic dermatitis, allergic rhinitis and several ocular allergic diseases. Allergic reactions may generally be divided into two components; the early phase reaction, and the late phase reaction.
Type III hypersensitivity. Type III hypersensitivity, in the Gell and Coombs classification of allergic reactions, occurs when there is accumulation of immune complexes ( antigen - antibody complexes) that have not been adequately cleared by innate immune cells, giving rise to an inflammatory response and attraction of leukocytes.