What is an allergy?
An allergy refers to an exaggerated reaction by our immune system in response to exposure to certain foreign substances. It is exaggerated because these foreign substances are usually seen by the body as harmless and no response occurs in nonallergic people. In allergic individuals, the body recognizes the foreign substance and one arm of the immune system generates a response.
Allergy-producing substances are called "allergens." Examples of allergens include pollens, dust mites, molds, animal proteins, foods, and even medications. To understand the language of allergy it is important to remember that allergens are substances that are foreign to the body and can cause an allergic reaction in certain people. When an allergic individual comes in contact with an allergen, the immune system mounts a response through the IgE antibody. Therefore, people who are prone to allergies are said to be allergic or "atopic."
Austrian pediatrician Clemens Pirquet (1874-1929) first used the term allergy. He referred to both immunity that was beneficial and to the harmful hypersensitivity as "allergy." The word allergy is derived from the Greek words "allos," meaning different or changed and "ergos," meaning work or action. Generally speaking, allergy therefore refers to an "altered reaction." The word allergy was first used in 1905 to describe the adverse reactions of children who were given repeated shots of horse serum to fight infection. The following year, the term allergy was proposed to explain this unexpected "changed reactivity."
An allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid. Allergy is one of four forms of hypersensitivity and is formally called type I (or immediate) hypersensitivity. Allergic reactions are distinctive because of excessive activation of certain white blood cells called mast cells and basophils by a type of antibody called Immunoglobulin E (IgE). This reaction results in an inflammatory response which can range from uncomfortable to dangerous.
Mild allergies like hay fever are very common in the human population and cause symptoms such as red eyes, itchiness, and runny nose, eczema, hives, or an asthma attack. Allergies can play a major role in conditions such as asthma. In some people, severe allergies to environmental or dietary allergens or to medication may result in life-threatening reactions called anaphylaxis. Food allergies, and reactions to the venom of stinging insects such as wasps and bees are often associated with these severe reactions.
A variety of tests exist to diagnose allergic conditions. If done they should be ordered and interpreted in light of a person's history of exposure as many positive test results do not mean a clinically significant allergy.Tests include placing possible allergens on the skin and looking for a reaction such as swelling and blood tests to look for an allergen-specific IgE.
Treatments for allergies include avoiding known allergens, steroids that modify the immune system in general, and medications such as antihistamines and decongestants which reduce symptoms. Many of these medications are taken by mouth, although epinephrine, which is used to treat anaphylactic reactions, is injected. Immunotherapy uses injected allergens to desensitize the body's response.
Allergy facts
- Allergy involves an exaggerated response of the immune system, often to common substances such as foods or pollen.
- The immune system is an intricate system that defends the body against foreign invaders, such as bacteria and viruses, while also surveying for conditions such as cancer and autoimmunity.
- Allergens are substances that are foreign to the body and can cause an allergic reaction.
- IgE is the allergic antibody.
- Allergies can not only develop at any age, but many individuals also outgrow allergies over time.
- A person has a greater risk of developing allergic conditions if there is a family history of allergy, especially in their parents or siblings, but the environment also plays a role.
In this review you will learn how allergy relates to the immune system. You will begin understanding how and why certain people become allergic. The most common allergic diseases are discussed briefly in this article.
