Allergy is an
overreaction of the immune system. People
who have allergies experience reactions to
environmental or ingested substances that
are normally harmless to most individuals.
These substances are called allergens.
Re-exposure to these allergens, such as
pollen, causes the immune system to react.
The body, due to heredity and interaction
with the environment, produce specific types
of antibody, called IgE, to fight the
allergen. The antibodies attach to a blood
cell called a mast cell. Mast cells are
plentiful in the airways and in the
gastrointestinal tract where allergens tend
to enter the body. The mast cells explode
releasing a variety of chemicals including
histamine, which causes the symptoms of
allergy. Allergies might result in allergic
rhinitis, allergic conjunctivitis,
gastrointestinal difficulties, asthma,
hives, and a severe form of an allergic
reaction - anaphylaxis, which is life