Allergy is a disorder of the immune
system often also referred to as atopy. Allergic
reactions occur to normally harmless environmental substances
known as allergens; these reactions are acquired, predictable,
and rapid. Strictly, allergy is one of four forms of hypersensitivity
and is called type I (or immediate) hypersensitivity. It is characterized
by excessive activation of certain white blood cells called mast
cells and basophils by a type of antibody known as IgE, resulting
in an extreme inflammatory response. Common allergic reactions
include eczema, hives, hay fever, asthma
attacks, food allergies, and reactions to the venom of stinging
insects such as wasps and bees.
allergies like hay fever are highly prevalent in the human population
and cause symptoms such as allergic conjunctivitis, itchiness,
and runny nose. 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
anaphylactic reactions and potentially death.
variety of tests now exist to diagnose allergic conditions; these
include testing the skin for responses to known allergens or analyzing
the blood for the presence and levels of allergen-specific IgE.
Treatments for allergies include allergen avoidance, use of anti-histamines,
steroids or other oral medications, immunotherapy to desensitize
the response to allergen, and targeted therapy.
medical specialty concerned with allergies is allergology.