allergy, hypersensitive reaction of the body tissues of certain individuals to certain substances that, in similar amounts and circumstances, are innocuous to other persons. Allergens, or allergy-causing substances, can be airborne substances (e.g., pollens, dust, smoke), infectious agents (bacteria, fungi, parasites), foods (strawberries, chocolate, eggs), contactants (poison ivy, chemicals, dyes), or physical agents (light, heat, cold). It is believed that a person who is hereditarily predisposed toward allergy produces, when sensitized, special weak types of antibodies, called reagins, that give little immune protection but cause local tissue damage during the antibody-antigen reaction (see immunity immunity, ability of an organism to resist disease by identifying and destroying foreign substances or organisms. Although all animals have some immune capabilities, little is known about nonmammalian immunity.
..... Click the link for more information. ). Allergens can affect the respiratory system, the reaction manifesting itself as asthma or hay fever, or they can affect the skin, causing wheals and rashes. Allergens may also act on the gastrointestinal tract, causing nausea and vomiting. Allergic reactions to substances injected into the bloodstream can cause violent and sometimes fatal reactions (see anaphylaxis anaphylaxis (ăn'əfəlăk`sĭs)
..... Click the link for more information. ; serum sickness serum sickness, hypersensitive response that occurs after injection of a large amount of foreign protein. The condition is named for the serum taken from horses or other animals immunized against a particular disease, e.g., tetanus or diphtheria.
..... Click the link for more information. ). The best treatment of allergic reactions is prevention, i.e., elimination of the offending substances from the sensitive person's environment. If this is not possible, desensitization (i.e., deliberate production of the allergic reaction by injecting the allergen, after which the sufferer is no longer susceptible) is sometimes helpful. Antihistamine drugs may give temporary relief. See histamine histamine (hĭs`təmēn')
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allergy

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.

allergy (redirected from allergic)

allergy

allergy
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