1. Hypersensitivity caused by exposure to a particular antigen (allergen) resulting in a marked increase in reactivity to that antigen upon subsequent exposure, sometimes resulting in harmful immunologic consequences. SYN: acquired sensitivity, induced sensitivity. SEE ALSO: allergic reaction, anaphylaxis, immune. 2. That branch of medicine concerned with the study, diagnosis, and treatment of allergic manifestations. 3. An acquired hypersensitivity to certain drugs and biologic materials. [G. allos, other, + ergon, work]
- bacterial a. 1. type I hypersensitivity allergic reaction caused by bacterial allergens; 2. the delayed type of skin test (type IV hypersensitivity reaction), so-called because of its early association with bacterial antigens ( e.g., the tuberculin test).
- cold a. physical symptoms produced by hypersensitivity to cold.
- contact a. SYN: allergic contact dermatitis.
- delayed a. a type IV hypersensitivity allergic reaction; so called because in a sensitized subject the reaction becomes evident hours after contact with the allergen (antigen), reaches its peak after 24–48 hours, then recedes slowly. Associated with cell-mediated responses. SEE ALSO: delayed reaction. Cf.:immediate a..
- immediate a. a type I hypersensitivity allergic reaction; so called because in a sensitized subject the reaction becomes evident usually within minutes after contact with the allergen (antigen), reaches its peak within an hour or so, then rapidly recedes. SEE ALSO: immediate reaction, anaphylaxis. Cf.:delayed a..
- latent a. a. that causes no signs or symptoms but can be revealed by means of certain immunologic tests with specific allergens.
- physical a. excessive response to factors in the environment such as heat or cold.
- polyvalent a. allergic response manifested simultaneously for several or numerous specific allergens.

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al·ler·gy 'al-ər-jē n, pl -gies
1) altered bodily reactivity (as hypersensitivity) to an antigen in response to a first exposure <his bee-venom \allergy may render a second sting fatal>
2) exaggerated or pathological reaction (as by sneezing, respiratory embarrassment, itching, or skin rashes) to substances, situations, or physical states that are without comparable effect on the average individual
3) medical practice concerned with allergies

* * *

a disorder in which the body becomes hypersensitive to particular antigens (called allergen), which provoke characteristic symptoms whenever they are subsequently inhaled, ingested, injected, or otherwise contacted. Normally antibodies in the bloodstream and tissues react with and destroy specific antigens without further trouble. In an allergic person, however, the allergens provoke the release of a class of antibodies (IgE) that become bound to mast cell in the body's tissues. The subsequent reaction of allergen with tissue-bound antibody (see reagin) also leads, as a side-effect, to cell damage, release of histamine and serotonin (5-hydroxytryptamine), inflammation, and all the symptoms of the particular allergy. Different allergies afflict different tissues and may have either local or general effects, varying from asthma and hay fever to severe dermatitis or gastroenteritis or extremely serious shock (see anaphylaxis).
allergic adj.

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al·ler·gy (alґər-je) [all- + ergon work] 1. a state of hypersensitivity induced by exposure to a particular antigen (allergen) resulting in harmful immune responses on subsequent exposures; the term is usually used to refer to hypersensitivity to an environmental antigen (atopic allergy or contact dermatitis) or to drug allergy. 2. The medical specialty dealing with diagnosis and treatment of allergic disorders. allergic adj

Medical dictionary. 2011.

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