Allergy : (noun)
1: hypersensitivity reaction to a particular allergen; symptoms
can vary greatly in intensity [syn: allergic reaction]
Based on WordNet 2.0
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Allergy : Allergy: A misguided reaction to foreign substances by the atopic .
Although allergies can develop at any age, the risk of developing allergies is genetic. It is related to ones family history of allergy. If neither parent is allergic, the chance for allergies
is about 15%. If one parent is allergic, the risk increases to 30% and if both are allergic, the risk is greater than 60%.
Allergens cause the production of immunoglobulin E (IgE), an antibody that all of us have in small amounts. Allergic persons, however, produce IgE in abnormally quantities. Normally, this antibody
is important in protecting us from parasites, but not from other allergens. During the sensitization period in allergy, IgE is overproduced. It coats certain potentially explosive cells that contain
chemicals including histamine. These chemicals, in turn, cause inflammation and the typical allergic symptoms. This is how the immune system becomes misguided and primed to cause an allergic reaction
when stimulated by an allergen.
The most common allergic conditions include shock (also called anaphylaxis and anaphylactic shock). For a thumbnail sketch of each of these conditions:
Hay fever (allergic rhinitis) is the most common of the allergic diseases and refers to seasonal nasal symptoms that are due to pollens. Year round or perennial allergic rhinitis is usually
due to indoor allergens , such as dust mites or molds. Symptoms result from the inflammation of the tissues that line the inside of the nose (mucus lining or membranes) after allergens are inhaled.
Adjacent areas, such as the ears, sinuses, and throat can also be involved. The most common symptoms include: - Runny nose
- Stuffy nose
- Sneezing
- Nasal itching (rubbing)
- Itchy
ears and throat
- Post nasal drip (throat clearing)
Asthma is a breathing problem that results from the inflammation and spasm of the lung's air passages (bronchial tubes). The inflammation causes a narrowing of the air passages, which limits
the flow of air into and out of the lungs. Asthma is most often, but not always, related to allergies. Common symptoms include: - Shortness of breath
- Wheezing
- Coughing
- Chest
tightness
Allergic eyes (allergic conjunctivitis) is inflammation of the tissue layers (membranes) that cover the surface of the eyeball and the undersurface of the eyelid. The inflammation occurs a
result of an allergic reaction and features: - Redness under the lids and of the eye overall
- Watery, itchy eyes
- Swelling of the membranes
Allergic eczema is an allergic rash that is usually not caused by skin contact with an allergen and features the following symptoms: - Itching, redness, and or dryness of the skin
- Rash on the face, especially children
- Rash around the eyes, in the elbow creases, and behind the knees, especially in adults
Hives (urticaria) are skin reactions that appear as itchy swellings and can occur on any part of the body. Hives can be caused by an allergic reaction, such as to a food or medication, but
they also may occur in non-allergic people. Typical hive symptoms are: - Raised red welts
- Intense itching
Allergic shock ( Low blood pressure or shock
For additional information on allergies, please read the Allergy article.
Based on University of Miami School of Medicine [Medical_Dictionary]:
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Allergy : Introduction
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.
What does an allergy mean?
An allergy refers to a misguided reaction by our immune system in response to bodily contact with certain foreign substances. It is misguided because
these foreign substances are usually harmless and remain so to non- allergic people. Allergy-producing substances are called "allergens." Examples of allergens include pollens, dust mite, molds,
danders, and foods. 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 allergen comes in contact with the body, it causes the immune system to develop an allergic reaction in persons who are allergic to it. When you inappropriately react to allergens that are
normally harmless to other people, you are having an allergic reaction and can be referred to as allergic or atopic. 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. Allergy roughly 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." Allergy Fact - It is estimated that 50 million North Americans are affected by allergic conditions.
- The cost of allergies in the United States is more
than $10 billion dollars yearly.
- Asthma affects 15 million Americans, 5 million of whom are children.
- The number of cases of asthma has doubled over the last 20 years.
How do allergies develop?
To help answer this question, let's look at a common household example. A few months after the new cat arrives in the house, dad begins to have itchy
eyes and episodes of sneezing. One of the three children develops coughing and wheezing, especially when the cat comes into her bedroom. The mom and the other two children experience no reaction
whatsoever to the presence of the cat. How can we explain this?
The immune system is the body's organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called
antigens. Antigens are substances that are capable of causing the production of antibodies. Antigens may or may not lead to an allergic reaction. Allergens are certain antigens that cause an allergic
reaction and the production of IgE.
The aim of the immune system is to mobilize its forces at the site of invasion and destroy the enemy. One of the ways it does this is to create protective proteins called antibodies that are
specifically targeted against particular foreign substances. These antibodies, or immunoglobulins (IgG, IgM, IgA, IgD), are protective and help destroy a foreign particle by attaching to its surface,
thereby making it easier for other immune cells to destroy it. The allergic person however, develops a specific type of antibody called immunoglobulin E, or IgE, in response to certain normally
harmless foreign substances, such as cat dander. To summarize, immunoglobulins are a group of protein molecules that act as antibodies. There are 5 different types; IgA, IgM, IgG, IgD, and IgE. IgE is
the allergy antibody.
(In 1967, the husband and wife team of Kimishige and Teriko Ishizaka detected a previously unrecognized type of immunoglobulin in allergic people. They called it gamma E globulin or IgE.)
In the pet cat example, the dad and the youngest daughter developed IgE antibodies in large amounts that were targeted against the cat allergen, the cat dander. The dad and daughter are now
sensitized or prone to develop allergic reactions on subsequent and repeated exposures to cat allergen. Typically, there is a period of "sensitization" ranging from months to years prior to an allergic
reaction. Although it might occasionally appear that an allergic reaction has occurred on the first exposure to the allergen, there must have been a prior contact in order for the immune system to be
poised to react in this way.
IgE is an antibody that all of us have in small amounts. Allergic persons, however, produce IgE in large quantities. Normally, this antibody is important in protecting us from parasites, but not
from cat dander or other allergens. During the sensitization period, cat dander IgE is being overproduced and coats certain potentially explosive cells that contain chemicals. These cells are capable
of causing an allergic reaction on subsequent exposures to the dander. This is because the reaction of the cat dander with the dander IgE irritates the cells and leads to the release of various
chemicals, including histamine. These chemicals, in turn, cause inflammation and the typical allergic symptoms. This is how the immune system becomes misguided and primed to cause an allergic reaction
when stimulated by an allergen.
On exposure to cat dander, the mom and the other two children produce other classes of antibodies, none of which cause allergic reactions. In these non-allergic members of the family, the dander
particles are eliminated uneventfully by the immune system and the cat has no effect on them.
Figure 1
The Immune System
Foreign Substance
alt="-"
(cat dander, pollen, virus,
bacteria) |   | | Normal Immune Response IgM, IgG, IgA, IgD and various immune cells
respond to attack. | | Misguided Immune Response IgE is
overproduced in response to cat dander, pollens, and other harmless allergens. | | 
|
| | Foreign substance is eliminated. | Subsequent exposure results in an allergic
reaction. | |
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| | Non-Allergic Individual | Allergic Individual | |
Who is at risk and why?
Allergies can develop at any age, possibly even in the womb. They commonly occur in children but may give rise to symptoms for the first time in
adulthood. Asthma may persist in adults while nasal allergies tend to decline in old age.
Why, you may ask, are some people "sensitive" to certain allergens while most are not? Why do allergic persons produce more IgE than those who are non-allergic? The major distinguishing factor
appears to be heredity. For some time, it has been known that allergic conditions tend to cluster in families. Your own risk of developing allergies is related to your parents' allergy history. If
neither parent is allergic, the chance that you will have allergies is about 15%. If one parent is allergic, your risk increases to 30% and if both are allergic, your risk is greater than 60%.
Although you may inherit the tendency to develop allergies, you may never actually have symptoms. You also do not necessarily inherit the same allergies or the same diseases as your parents. It is
unclear what determines which substances will trigger a reaction in an allergic person. Additionally, which diseases might develop or how severe the symptoms might be is unknown.
Another major piece of the allergy puzzle is the environment. It is clear that you must have a genetic tendency and be exposed to an allergen in order to develop an allergy. Additionally, the more
intense and repetitive the exposure to an allergen and the earlier in life it occurs, the more likely it is that an allergy will develop.
There are other important influences that may conspire to cause allergic conditions. Some of these include smoking, pollution, infection, and hormones.
What are common allergic conditions?
The parts of the body that are prone to react to allergies include the eyes, nose, lungs, skin, and stomach. Although the various allergic
diseases may appear different, they all result from a misguided immune response to foreign substances in sensitive people. The following brief descriptions will serve as an overview of common allergic
disorders.
Hay Fever
Hay fever (Allergic Rhinitis) is the most common of the allergic diseases and refers to seasonal nasal symptoms that are due to pollens. Year round or perennial
allergic rhinitis is usually due to indoor allergens , such as dust mites or molds. Symptoms result from the inflammation of the tissues that line the inside of the nose (mucus lining or membranes)
after allergens are inhaled. Adjacent areas, such as the ears, sinuses, and throat can also be involved. The most common symptoms include: - Runny nose
- Stuffy nose
- Sneezing
- Nasal itching (rubbing)
- Itchy ears and throat
- Post nasal drip (throat clearing)
In 1819, an English physician, John Bostock, first described hay fever by detailing his own seasonal nasal symptoms, which he called "summer catarrh." The condition was called hay fever because it
was thought to be caused by "new hay."
Asthma
Asthma is a breathing problem that results from the inflammation and spasm of the lung's air passages (bronchial tubes). The inflammation causes a narrowing of the air
passages, which limits the flow of air into and out of the lungs. Asthma is most often, but not always, related to allergies. Common symptoms include: - Shortness of breath
- Wheezing
- Coughing
- Chest tightness
Allergic Eyes
Allergic Eyes (Allergic Conjunctivitis) is inflammation of the tissue layers (membranes) that cover the surface of the eyeball and the undersurface of the eyelid.
The inflammation occurs a result of an allergic reaction and may produce the following symptoms: - Redness under the lids and of the eye overall
- Watery, itchy eyes
- Swelling of the
membranes
Allergic Eczema
Allergic Eczema (Atopic Dermatitis) is an allergic rash that is usually not caused by skin contact with an allergen. This condition is commonly associated
with allergic rhinitis or asthma and features the following symptoms: - Itching, redness, and or dryness of the skin
- Rash on the face, especially children
- Rash around the eyes, in
the elbow creases, and behind the knees, especially in adults
Hives
Hives (Urticaria) are skin reactions that appear as itchy swellings and can occur on any part of the body. Hives can be caused by an allergic reaction, such as to a
food or medication, but they also may occur in non-allergic people. Typical hive symptoms are: - Raised red welts
- Intense itching
Allergic Shock
Allergic Shock Low blood pressure or shock
Shock refers to the insufficient circulation of blood to the body's tissues. Shock is most commonly caused by blood loss or an infection. Allergic shock is caused by dilated and "leaky" blood
vessels, which result in a drop in blood pressure.
Where are allergens? Everywhere
We have seen that allergens are special types of antigens that cause allergic reactions. The symptoms and diseases that result depend largely on
the route of entry and level of exposure to the allergens. The chemical structure of allergens affects the route of exposure. Airborne pollens, for example, will have little effect on the skin. They
are easily inhaled and will thus cause more nasal and lung symptoms and limited skin symptoms. When allergens are swallowed or injected they may travel to other parts of the body and provoke symptoms
that are remote from their point of entry. For example, allergens in foods may prompt the release of mediators in the skin and cause hives.
We will assume that allergens are defined as: the source of the allergy producing substance (e.g. Cat), the substance itself (cat dander), or the specific proteins that provoke the immune response
(e.g. Feld1). Feld1, from the Felis domesticus (the domesticated cat), is the most important chemical allergen in cat dander.
Allergens may be inhaled, ingested (eaten or swallowed), applied to the skin, or injected into the body either as a medication or inadvertently by an insect sting.
In The Air We Breathe
Breathing can be hazardous if you are allergic. Aside from oxygen, the air contains a wide variety of particles; some toxic, some infectious, and some
"innocuous," including allergens. The usual diseases that result from airborne allergens are hay fever, asthma, and conjunctivitis. The following allergens are usually harmless, but can trigger
allergic reactions when inhaled by sensitized individuals. - Pollens: trees, grasses, and/or weeds
- Dust mites
- Animal proteins: dander, skin, and/or urine
- Mold
spores
- Insect parts: cockroaches
In What We Ingest
When foods or medications are ingested, allergens may gain access to the blood stream and become attached to specific IgE on cells in remote sites such as the
skin or nasal membranes. The ability of allergens to travel explains how symptoms can occur in areas other than the gastrointestinal tract. diarrhea , or stomach cramps. Nasal breathing difficulties
or skin reactions may also be seen. The two main allergen groups that are ingested are: - Foods
- Drugs (when taken by mouth): e.g. antibiotics and aspirin
Allergy Assist The most common foods that cause allergic reactions are cow's milk, fish, shellfish, eggs, peanuts, tree nuts, soy, and wheat.
Touching Our Skin
Allergic contact dermatitis is an inflammation of the skin that is caused by a local allergic reaction. The majority of these localized skin reactions do not
involve IgE, but are caused by cells of inflammation. The rash produced is similar to that of a poison ivy rash. It should be noted that when some allergens (e.g., latex) come into contact with the
skin, they are absorbed by the skin and can also potentially cause reactions throughout the body, not just the skin. For most people, however, the skin is a formidable barrier that can be only locally
affected. Examples of allergic contact dermatitis include: - Latex (causes IgE and non-IgE reactions
- Plants (poison ivy and oak)
- Dyes
- Chemicals
- Metals
(nickel)
- Cosmetics
Allergic contact dermatitis does not involve IgE antibody, but involves cells of the immune system which are programmed to react when triggered by a sensitizing allergen. Touching or rubbing a
substance to which you were previously sensitized can trigger a skin rash.
Injected Into Our Body
The most severe reactions can occur when allergens are injected into the body and gain direct access to the blood stream. This access carries the risk of a
generalized reaction, such as anaphylaxis, which can be life-threatening. The following are commonly injected allergens that can cause severe allergic reactions: - Insect venom
- Medications
- Vaccines (including allergy shots)
- Hormones (e.g., Allergy At A Glance
- Allergy involves a misguided response of the immune system.
- The immune
system is the body's organized defense mechanism against foreign invaders, particularly infections.
- Allergens are substances that are foreign to the body and can cause an allergic reaction.
- IgE is the allergy antibody.
- Allergies can develop at any age.
- Your risk of developing allergies is related to your parents' allergy history.
Based on University of Miami School of Medicine [Medical_Dictionary]:
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