The dictionary makes “allergy” sound simple. Wiki dictionary defines allergy as “A condition of hypersensitivity to a substance (an allergen) considered harmless to most people. as difficulty breathing and / or swellings / rashes. ”

That does not sound like such a big problem, does it? But allergies are a big problem to those who suffer with them, and together the “difficulty breathing and / or swelling / rashes” part, in some cases death is actually a possibility as well.

Peanuts and shellfish are two known sources that cause violent allergic reactions in some people. When you become aware of these specific allergies you have to read labels at the supermarket. Many food products will contain peanuts. Manufactures are required to list peanuts as an ingredient even if it may be in very small amounts.

When you eat at restaurants you must inform the wait person of your allergy so they can recommend safe dishes for you. Shellfish, even the juice from shellfish if consumed by someone who is highly allergic can result in an ugly public incident. We have all heard of lawsuits being filed against a restaurant or wait staff for negligence.

In the most obvious terms, the immune systems of people who are allergic overreact when exposed to certain substances that the immune systems of most people have already built up immunity against.

It's the job of the immune system to defend the body from invaders germs, bacteria, or any foreign substance. This system is designed to attack and destroy substances that the body comes in contact with that the immune system considers dangerous. The problem of allergies arises when the bodies bodies an attack against perfectly harmless substances, such as grass pollen, cat dander, peanuts, penicillin, or any one of millions of other harmless substances.

The term, “allergy” was first used in 1906 to describe an altered reaction in the body's defense system. The word allergy comes from the Greek “allos,” which means “other.”

Our immune systems have a perfect memory and have total recall. If the immune system overacts to a substance once, it will always overreact. Our defenses identifies what it considers a dangerous invasion and develops antibodies to destroy it.

That's why someone who suffers from hay fever will react every time he comes in contact with that specific type of pollen that has been memorized by his immune system.