Allergy and immunology go hand-in-hand. Allergy has been defined as "adverse physiological events caused by a variety of immunologic reactions." Any organ of the body can be involved, but the most common "shock organs" are the nose, skin and lungs. In most cases, the immune system is protecting and acting as the body's natural defense against infections, ridding it of potentially dangerous substances which may disturb its normal internal environment. Such substances may be introduced from outside the body or generated from within.
An allergy is what happens when your body detects a foreign substance it doesn't like. Your nose may plug up and start dripping, your eyes may itch and run, your lungs may burn and produce wheezing.