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Definition of ALLERGY
: altered bodily reactivity (as hypersensitivity) to an antigen in response to a first exposure <a bee venom allergy so severe that a second sting may be fatal>
: exaggerated or pathological immunological reaction (as by sneezing, difficult breathing, itching, or skin rashes) to substances, situations, or physical states that are without comparable effect on the average individual
: altered bodily reactivity (as hypersensitivity) to an antigen in response to a first exposure <his bee-venom allergy may render a second sting fatal>
: 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
: medical practice concerned with allergies
Exaggerated reaction by the body to foreign substances that are harmless to most people. Those substances, called allergens or antigens, may include pollens, drugs, dusts, foods, and other items. Immediate allergic reactions result from genetic predisposition or sensitization by previous exposure. Blood vessels dilate and bronchial air passages constrict. A severe reaction (anaphylaxis) can obstruct breathing and may be fatal. Delayed allergic responses (e.g., contact dermatitis) appear 12 hours or more after exposure. Avoiding allergens and taking antihistamines can prevent or treat allergies. When avoidance is not feasible and antihistamines do not relieve symptoms, desensitization can be attempted.