People who are predisposed to allergies
produce excess IGE antibodies. When an
allergic person comes in contact with an
allergen, it can combine with a specific
IGE antibody which causes histamines,
leukotrienes, and other chemicals to be
released from cells in the body tissues.
This is what causes allergy reactions
like sneezing, itching, swelling of
tissues in the nose and airways, coughing,
wheezing, and other symptoms. 
Each type of IGE reacts with only one type of allergen.
That's why some people are only
allergic to cat dander
while others are allergic to many things.
During an asthma attack, your airways or
bronchial tubes constrict or tighten and
may become inflamed in response to
certain triggers. This means the lining
of the tubes that bring air to the lungs
is swollen which makes it more difficult
for air to move freely in and out. Glands
in the lining of your airways may
produce extra mucus which accumulates 
in these already narrowed tubes and
contribute to the problem.
