The word 'allergy' is frequently misused and applied indiscriminately to any adverse reaction, regardless of the mechanism. An allergic response is a reproducible adverse reaction to a substance mediated by an immunological response. The substance provoking the reaction may have been ingested, injected, inhaled, or merely have come into contact with the skin or mucous membranes. Food allergy is a form of adverse reaction to food in which the cause is an immunological response to a food. The much broader term of 'food intolerance' does not imply any specific type of mechanism and is simply defined as a reproducible adverse reaction to a specific food or food ingredient. Outside the United Kingdom, the terminology used sometimes differs. It has been suggested that the term 'food hypersensitivity' should be used to cover all adverse reactions to food, which are then subdivided into food allergy (i.e., immuno-logically mediated) and food intolerance, which implies a nonimmunologically mediated event.

The term 'food aversion' comprises food avoidance, where the subject avoids a food for psychological reasons such as distaste or a desire to lose weight, and psychological intolerance. The latter is an unpleasant bodily reaction caused by emotions associated with the food rather than the food itself. Psychological intolerance will normally be observable under open conditions but will not occur when the food is given in an unrecognizable form. Psychological intolerance may be reproduced by suggesting (falsely) that the food has been administered.

The term 'anaphylaxis' or 'anaphylactic shock' is taken to mean a severe and potentially life-threatening reaction of rapid onset with circulatory collapse. The term anaphylaxis has also been used to describe any allergic reaction, however mild, that results from specific IgE antibodies, but such usage fails to distinguish between a trivial reaction (e.g., a sneeze) and a dangerous event.

An antigen is a substance that is capable of provoking an immune response. An antibody is an immunoglobulin that is capable of combining specifically with certain antigens. An allergen is a substance that provokes a harmful (allergic) immune response.

Immunological tolerance is a process that results in the immunological system becoming specifically unreactive to an antigen that is capable in other circumstances of provoking antibody production or cell-mediated immunity. The immunological system nevertheless reacts to unrelated antigens given simultaneously and via the same route.

Atopy is the ability to produce a weal-and-flare response to skin prick testing with a common antigen, such as house dust mite or grass pollen. The atopic diseases are asthma (all childhood cases but not all adult cases), atopic eczema, allergic rhinitis, allergic conjunctivitis, and some cases of urticaria.

Food Allergies

Food Allergies

Peanuts can leave you breathless. Cat dander can lead to itchy eyes, a stuffy nose, coughing and sneezing. And most of us have suffered through those seasonal allergies with horrible pollen counts. Learn more...

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