What is an allergy?

?What is an allergy

The word allergy refers to a reaction to an environmental

substance, either by breathing it, eating it, or having

contact with the skin. The most common mechanism by

which an environmental substance causes this kind of

reaction involves antibodies, which are proteins formed

by the immune system. The normal function of antibodies

is to protect the body from infection by attacking

and killing organisms like viruses and bacteria. In the

case of allergy, the antibody is called immunoglobulin E,

or IgE, and, rather than attaching itself to microorganisms,

the antibody binds to normally harmless substances

like pollen, dust mites, and animal danders.

Once IgE is formed in the bloodstream, it seeks out

and binds to a type of cell called a mast cell, which is

located in the mucous membrane of the eyes, nose,

lungs, and gastrointestinal tract as well as skin. If the

person is then reexposed to that same allergen, the mast

cell is triggered within a few minutes to release a variety

of chemicals, including histamines, leukotrienes, and

prostaglandins (Table 1). These chemicals, which are

also referred to as mediators of the allergic response,

are responsible for the symptoms that patients develop after

exposure to allergens.

Table 1 Chemicals Involved in Allergic Reactions