Allergy
Allergy is a disorder of the immune
system that is often called atopy. Allergic reactions occur to 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, food allergies,
and reactions to the venom of stinging insects such as wasps and bees.
Mild allergies like hay
fever, are highly prevalent in the human population and cause symptoms such
as allergic conjunctivitis, itchiness and runny nose. Similarly, conditions
such as asthma are common, in which allergy plays a major role. In some people,
severe allergies to environmental or dietary allergens, or to medication,
occur that may result in life-threatening anaphylactic reactions and potentially
death.A 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 antihistamines, steroids or other oral medications, immunotherapy
to desensitize the response to allergen, and targeted therapy.
Causes
Risk factors for allergy can be placed in two general categories, namely host
and environmental factors. Host factors include heredity, sex, race and age,
with heredity being by far the most important. There are recent increases
in the incidence of allergic disorders, however, that cannot be explained
by genetic factors alone. The four main candidate environmental factors are
alterations in exposure to infectious diseases during early childhood, environmental
pollution, allergen levels, and dietary changes.