Allergy 101

What is an allergy?
The basic explanation:
Allergies result from a “mistaken immune response” in which antibodies are made against substances (allergens) that are harmless to non-allergic people. 
The technical explanation:
An antigen is any substance that is capable of causing your body's immune system to produce antibodies (or sometimes certain types of cells). Antibodies are gamma globulins in your blood. 

When you are subsequently exposed to the same antigen, the antigen and antibodies interact, which can result in various outcomes depending upon the nature of the antigen and antibodies. 

Allergens are a special category of antigens. Like other antigens, they elicit antibody production. But only people with allergic tendencies respond to them by producing “allergic antibodies.”
When you start making allergic antibodies to something, we say that you have become “sensitized” to that substance. And once you are sensitized to something, you will experience allergic reactions when you are exposed to it again.
Why do I have allergies?
Nobody knows exactly why we develop allergies. In fact, I like to refer to allergies as an “immunological mistake.” 

The same substances that are allergens for people with allergies typically don't cause problems for people without allergies. Non-allergic people can breathe in the same microscopic bits of organic matter and eat the same foods to which allergic people react and have no problems. 

It certainly seems that people with allergies would be better off if their immune systems would just ignore the substances to which they are allergic.
Allergies are common
Allergy is our country’s single most common health problem and is responsible for more time lost from work and school than any other medical condition. It also limits social and athletic activities above all else—including high blood pressure, diabetes, high cholesterol, cancer, etc.
Who gets allergies?
Most kinds of allergy are hereditary. If there are allergies on both sides of your family, you have about an 80% chance of having sensitivities yourself. But the particular pattern of allergic responses and the substances responsible can vary a great deal from one family member to the next. 

For example, mom might have nasal allergy while son has skin or lung problems. And dad might be allergic to tree and weed pollens while daughter is allergic only to mold spores or particular foods. 

If you have inherited the tendency to develop allergies, you can experience their initial onset at any age. It isn't necessary to have had allergies during childhood to have them as an adult. 

But even if you are predisposed toward developing allergies, you might never experience their onset. 

Although there is a lot of speculation, the reasoning behind why susceptible people can develop allergy problems later in life is still unknown.