Allergy involves an exaggerated response of the immune system, often to common substances .

1. Allergy
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 normally 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.
Although many individuals outgrow allergies over time, allergies can also develop at any age, including during adulthood.
While environment plays a role in allergy development, there is a greater risk of developing allergic conditions if a person has a family history of allergy, especially in parents or siblings.

2. Allergy prevalence
Approximately 10% 30% of individuals in the industrialized world are affected by allergic conditions, and this number is increasing.
Allergic rhinitis (nasal allergies) affects roughly 20% of Americans. Between prescription costs, physician visits, and missed days of work/school, the economic burden of allergic disease exceeds $3 billion annually.
Asthma affects roughly 8% 10% of Americans. The estimated health costs for asthma exceed approximately $20 billion annually.
Food allergies affect roughly 3% 6% of children in the United States, and roughly 1% 2% of adults in the U.S.

3. causes allergies
To help answer this question, lets 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. The mom and the other two children experience no reaction whatsoever despite the presence of the cat. How can we explain this?
The immune system is the bodys organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called antigens. Antigens often lead to an immune response through the production of antibodies, which are protective proteins that are specifically targeted against particular antigens. These antibodies, or immunoglobulins (IgG, IgM, and IgA), 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. Other antigens, such as bacteria, do not lead to production of IgE, and therefore do not cause allergic reactions. IgE was discovered and named in 1967 by Kimishige and Teriko Ishizaka.

4. Risk for allergies
Allergies can develop at any age, and the initial exposure or sensitization period may even begin in while the fetus is in the uterus. Individuals can also outgrow allergies over time. Whereas many children outgrow food allergies, nasal or environmental allergies often develop over time.
Why, you may ask, are some people sensitive to certain allergens while most are not? Why do allergic people produce more IgE than those who are nonallergic? Although we certainly do not fully understand why one person develops allergies and another does not, we know there are several risk factors for allergic conditions. Family history, or genetics, plays a large role, with a higher risk for allergies if parents or siblings have allergies. There are numerous other risk factors for developing allergic conditions. Children born via Cesarean section have a higher risk of allergy as compared to children who are delivered vaginally. Exposure to tobacco smoke increases the risk of allergy. Boys are more likely to be allergic than girls. Exposures to antigens, use of antibiotics, and numerous other factors, some of which are not yet known, also contribute to the development of allergies. This complicated process continues to be an area of medical research.

5. common allergic
The parts of the body that are prone to allergic symptoms include the eyes, nose, lungs, skin, and gastrointestinal tract. Although the various allergic diseases may appear different, they all result from an exaggerated immune response to foreign substances in sensitive individuals. The following are brief descriptions of common allergic disorders.

6. Allergic rhinitis
Allergic rhinitis (hay fever) is the most common of the allergic diseases and refers to nasal and ocular symptoms that are due to aeroallergens. Year round or perennial allergic rhinitis is usually caused by indoor allergens, such as dust mites, animal dander, or molds. Seasonal allergic rhinitis is typically caused by tree, grass, or weed pollens. Many individuals have a combination of both seasonal and perennial allergies. Symptoms result from the inflammation of the tissues that line the inside of the nose after exposure to allergens. Adjacent areas, such as the eyes, ears, sinuses, and throat can also be involved.

7. Asthma
Asthma is a respiratory condition that results from inflammation and hyperreactivity of the airways, leading to recurrent, reversible constriction of the airways. Asthma can often coexist with allergic rhinitis. Other common triggers include respiratory viral infections and exercise.

8. Allergic eyes
Allergic eyes (conjunctivitis) are inflammation of the tissue layers (membranes) that cover the surface of the eyeball and the undersurface of the eyelid. The inflammation occurs as a result of an allergic reaction and may produce the following symptoms, which are generally present in both eyes.

9. Eczema
Eczema (atopic dermatitis) is a condition commonly found in individuals with other allergic conditions (asthma and allergic rhinitis) but is not usually caused by direct allergen exposure. The rash results from a complicated inflammatory process.

10. Hives
Hives (urticaria) are skin reactions that appear as red, raised, itchy welts and can occur on any part of the body. Short lived (acute) hives are often due to an allergic reaction to a food or medication, though they commonly result from a viral infection in children. Hives that recur over a longer period of time (chronic hives) are rarely due to an allergic reaction, and the underlying cause is typically more complicated.

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