What are allergies?
Basic Information on Allergies
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Allergy - Wikipedia, the free encyclopedia
** Allergy **
From Wikipedia, the free encyclopedia
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/Classification and external resources/
Hives are a common allergic symptom.
An *allergy* is a hypersensitivity disorder of the immune system.^
Allergic reactions occur when a person's immune system reacts to normally
harmless substances in the environment. A substance that causes a reaction
is called an allergen. These reactions are acquired, predictable, and
rapid. Allergy is one of four forms of hypersensitivity and is formally
called /type I/ (or /immediate/) hypersensitivity. Allergic reactions are
distinctive because of excessive activation of certain white blood cells
called mast cells and basophils by a type of antibody called Immunoglobulin
E (IgE). This reaction results in an inflammatory response which can range
from uncomfortable to dangerous.
Mild allergies like hay fever are very common in the human population and
cause symptoms such as red eyes, itchiness, and runny nose, eczema, hives,
or an asthma attack. Allergies can play a major role in conditions such as
asthma. In some people, severe allergies to environmental or dietary
allergens or to medication may result in life-threatening reactions called
anaphylaxis. Food allergies, and reactions to the venom of stinging insects
such as wasps and bees are often associated with these severe
A variety of tests exist to diagnose allergic conditions. If done they
should be ordered and interpreted in light of a person's history of
exposure as many positive test results do not mean a clinically significant
allergy.^ Tests include placing possible allergens on the skin and
looking for a reaction such as swelling and blood tests to look for an
Treatments for allergies include avoiding known allergens, steroids
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