Allergies: You either have one, or you know someone who does. They are common, and sometimes lethal.

But what is an allergy? Why do some people have allergies, and others seem to be completely free of any symptoms?

What is an allergy?
An allergy is defined by Webster's Dictionary as "an abnormal reaction of the body to a previously encountered allergen introduced by inhalation, ingestion, injection, or skin contact, often manifested by itchy eyes, runny nose, wheezing, skin rash, or diarrhea."

Allergens are things in our environment and can be very common substances. The most common allergy is hayfever, which is a reaction to pollen, and the medical community estimates that about 20% of the people in the United States suffer from the condition.

Allergens can also include such substances as foods, drugs, chemicals, and secretions from plants virtually anything you encounter on a day-to-day basis can become an allergen. Common allergies along those lines include allergies to peanuts, penicillin, and poison ivy.

Why some people are predisposed to certain allergies has been studied in a formal way for over 100 years, ever since Viennese pediatrician Clemens von Pirquet kept records on his young patients and coined the word. They "why" still remains a partial mystery.

What causes an allergy?
Allergic reactions are caused by antibodies. They start the first time your body senses an allergen, and create antibodies against that specific chemical so your body will respond more quickly to a second exposure.

Creation of antibodies is normal. Without this reaction, people would catch diseases like the measles or chicken pox over and over again. When you get exposed to a substance, the body creates antibodies that float around your body much like a military patrol guarding the perimeter. This is the same general mechanism that allows vaccines to work, by exposing our bodies to either dead or weakened viruses, or proteins that are unique to certain germs.

People with allergies produce much greater levels of antibodies than normal, so the response the next time they are exposed to that allergen is much bigger than it should be. Symptoms can range from a simple runny nose, to anaphylactic shock and death.

Allergies are even (rarely) built into some people's genes, making allergies impossible to avoid for those people afflicted with this genetic quirk.

Can I avoid acquiring an allergy?
The answer is: maybe.

Some people are born prone to developing an allergy to certain substances, and a single exposure can be enough to create one. Sometimes an allergy can even be acquired in the womb, if the mother is exposed repeatedly to something that gets into her blood stream, and gets to the developing fetus.

Can I get rid of an allergy once I have it?
Again the answer is maybe.

Hypoensitization (immunotherapy) can be successfully used for certain individuals for certain allergies. This involves injecting larger and larger doses of the allergen into the body until the immune response, and creation of the large numbers of antibodies, is exhausted' and the overabundance of those antibodies no longer occurs.

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