We got some information from the Compton's Encyclopedia about allergies. We also have included a National Geographic that has an article about pollen allergies. It's yours to keep and share with your classmates. But, to give you a simple answer, some people's bodies think that things like pollen are foreign objects that have to be destroyed. The chemicals that the body has to fight off these substances cause the reactions that we call allergies.

From the encyclopedia:

Some people suffer from hay fever when pollen is in the air. Others develop skin rashes when they touch certain substances. Still others experience stomach cramps after eating particular foods. These ailments are all caused by allergic reactions to various substances. In most cases, an allergy causes relatively mild symptoms such as sneezes from breathing dust. A rare and severe allergic reaction can trigger anaphylactic shock that occasionally leads to death. Death from bee stings is an example of this severe type of allergic reaction.

An allergy develops in much the same way as does an immunity against an infectious disease (see Disease, section on infectious diseases). Several things happen to cause an allergy. First, a person is exposed to a substance such as pollen. The bodies of most people simply ignore pollen, but others treat pollen as a foreign invader. When this happens, a substance in the blood known as an antigen becomes active. Antigens cause the formation of antibodies whose job it is to fight off the invading substance.

Antibodies are normally in the blood and are activated by the antigen to which each is specifically linked. For instance, if a person who is allergic to shrimp eats the food, an antigen to shrimp will cause the formation of antibodies whose only function is to work against that one antigen.

Antigens that cause allergies are called allergens. The most common of these include dust, pollens, foods, animal danders (bits of dry skin or fur), insect venoms, cosmetics, soap, and drugs. Heat, cold, sunlight, and the emotions can also act as allergens.

Of the two people in ten who have some sort of allergy, many belong to families in which parents and other close relatives also have allergies. An inherited tendency to asthma, for instance, appears to be quite common. Specific allergies, such as those to pollen, are not inherited. A person becomes sensitive, or allergic, to pollen as a result of exposure to it.

Excerpted from Compton's Interactive Encyclopedia. Copyright (c) 1994, 1995, 1996 SoftKey Multimedia Inc. All Rights Reserved