Allergies: Overview

Allergies occur when the immune system responds to a substance. Common examples include dust allergies, pollen allergies (causing hay fever and respiratory allergies) and food allergies. But there are many other types of allergy. An allergic reaction can be dangerous when it leads to an anaphylactic reaction (anaphylaxis, anaphylactic shock). The substance that the body reacts to is called an Allergen (e.g. Pollen, Dust, Animal Hair, Dander, etc.). An allergic reaction needs to be distinguished from other types of body reactions to substances, such as an “intolerance” (e.g. food intolerances vs food allergies) or adverse reaction (e.g. poisoning, overdose, etc.).

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Back to: « Allergies

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Asthma and allergic diseases, such as allergic rhinitis (hay fever), food allergy, and atopic dermatitis (eczema), are common for all age groups in the United States. For example, asthma affects more than 17 million adults and more than 7 million children. Hay fever, respiratory allergies, and other allergies affect approximately 10 percent of children under 18 years old. In addition, food allergy affects an estimated 5 percent of children under 5 years old and 4 percent of children ages 5 to 17 years old and adults.

Source: NIAID (NIH)1

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Allergies are a form of hypersensitivity reaction, typically in response to harmless environmental allergens like pollen or food. Hypersensitivity reactions are divided into four classes. Class I, II, and III are caused by antibodies, IgE or IgG, which are produced by B cells in response to an allergen. Overproduction of these antibodies activates immune cells like basophils and mast cells, which respond by releasing inflammatory chemicals like histamine. Class IV reactions are caused by T cells, which may either directly cause damage themselves or activate macrophages and eosinophils that damage host cells.

Source: NIAID (NIH)2

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Allergies and Asthma (AZ-ma)

Slightly more than half of the 300 million people living in the U.S. are sensitive to one or more allergens.* They sneeze, their noses run and their eyes itch from pollen, dust and other substances. Some suffer sudden attacks that leave them breathless and gasping for air. This is allergic asthma. Asthma attacks often occur after periods of heavy exercise or during sudden changes in the weather. Some can be triggered by pollutants and other chemicals in the air and in the home. Doctors can test to find out which substances are causing reactions. They can also prescribe drugs to relieve the symptoms.

*Prevalences of Positive Skin Test Responses to 10 Common Allergens in the U.S. Population: Results from the Third National Health and Nutrition Examination Survey” Jour. Allergy Clinical Immunol. August 2005.

Source: NIEHS (NIH)3

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An allergy is a reaction by your immune system to something that does not bother most other people. People who have allergies often are sensitive to more than one thing. Substances that often cause reactions are

Normally, your immune system fights germs. It is your body's defense system. In most allergic reactions, however, it is responding to a false alarm. Genes and the environment probably both play a role.

Allergies can cause a variety of symptoms such as a runny nose, sneezing, itching, rashes, swelling, or asthma. Allergies can range from minor to severe. Anaphylaxis is a severe reaction that can be life-threatening. Doctors use skin and blood tests to diagnose allergies. Treatments include medicines, allergy shots, and avoiding the substances that cause the reactions.

NIH: National Institute of Allergy and Infectious Diseases

Source: MedLinePlus (NIH)4

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A change in season can brighten your days with vibrant new colors. But blooming flowers and falling leaves can usher in more than beautiful backdrops. Airborne substances that irritate your nose can blow in with the weather. When sneezing, itchy eyes, or a runny nose suddenly appears, allergies may be to blame.

Source: NIH News in Health (NIH)5

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Allergy: An abnormal immune system response to any stimulus that can take any of 4 different types of reaction characteristics (Immediate/IgE-Mediated, Cytotoxic, Immune Complex-Mediated or Delayed/Cell-Mediated); the classic working definition used by most physicians only includes immediate response allergic reactions (IgE-Mediated).

Source: RDCRN (NCATS/NIH)6

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An allergy is your body's overreaction to something that usually doesn't bother most people.

For example, grasses, pollen and cat fur can cause trouble for some people.

Source: Queensland Health7

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Allergic reactions can be scary if you’ve never had one before. If you have a mild allergic reaction, which could include hives, itching, sneezing, or a runny nose, you should take an antihistamine if it’s available and monitor for more severe symptoms, Dr. Guerrerio said.

Source: MedLinePlus Magazine (NIH)8

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Allergic reactions occur when the body wrongly defends itself against something that is not dangerous.

A healthy immune system defends against invading bacteria and viruses. During allergic reactions, however, the immune system fights harmless materials, such as pollen or mold, by producing a special class of antibody called immunoglobulin E (IgE).

Source: MedLinePlus Magazine (NIH)9

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Allergic reactions occur when the body wrongly defends itself against something that is not dangerous. A healthy immune system defends against invading bacteria and viruses. During allergic reactions, however, the immune system fights harmless materials, such as pollen or mold, with production of a special class of antibody called immunoglobulin E (IgE).

Source: MedLinePlus Magazine (NIH)10

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Acute Allergic Reactions

An acute, or serious, allergic reaction that comes on rapidly and may result in death is called “anaphylaxis.” It can have many symptoms and affect different parts of the body. Symptoms can include itching, sneezing, difficulty breathing, and blood circulation problems. As a result, it is under-recognized and under-treated.

The most common trigger foods for anaphylaxis are peanuts, tree nuts, milk, eggs, fish, and crustaceans (shellfish).

To reduce the risk of anaphylaxis, it is essential that you avoid your specific trigger food. If you have a history of anaphylactic reactions to food, you should always carry an epinephrine auto-injector with you.

Source: MedLinePlus Magazine (NIH)11

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An allergy is when your body’s immune system reacts to normally harmless substances that it sees as harmful. The allergy-causing substances are called allergens.

Source: New Zealand Health12

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Learn about allergy symptoms and treatment, how to recognise a life-threatening allergic reaction (anaphylaxis), and more.

Source: New Zealand Health13

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An allergy is a reaction the body has to a particular food or substance.

Allergies are very common. They're thought to affect more than one in four people in the UK at some point in their lives.

They are particularly common in children. Some allergies go away as a child gets older, although many are lifelong. Adults can develop allergies to things they weren't previously allergic to.

Having an allergy can be a nuisance and affect your everyday activities, but most allergic reactions are mild and can be largely kept under control. Severe reactions can occasionally occur, but these are uncommon.

Source: NHS Choices UK14

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Allergies: Pertaining to, caused by, affected with or of the nature of allergy.15

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Allergies: An allergy is an immune response or reaction to substances that are usually not harmful.16

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Allergies: A hypersensitivity adverse event which results in an allergic response showing a marked increase in reactivity to an antigen upon subsequent exposure.17

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Fast Facts

  • Allergies are reactions of your immune system to one or more things in the environment.
  • The immune system is your body's defense system. In allergic reactions, however, it is responding to a false alarm.
  • Pollens and mold spores can cause seasonal allergies.
  • Allergies from pollens and molds can cause runny and blocked noses, sneezing, nose and eye itching, runny and red eyes rashes, or asthma. Allergies typically make you feel bad.
  • Source: National Institute of Allergy and Infectious Diseases

Source: MedLinePlus Magazine (NIH)18

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References

  1. Source: NIAID (NIH): niaid.nih.gov/ topics/ allergicdiseases/ Pages/ default.aspx
  2. Source: NIAID (NIH): niaid.nih.gov/ topics/ immunesystem/ Pages/ immuneDisorders.aspx
  3. Source: NIEHS (NIH): niehs.nih.gov/ health/ assets/ docs_a_e/ environmental_diseases_environmental_diseases_from_a_to_z_english_508.pdf
  4. Source: MedLinePlus (NIH): medlineplus.gov/ allergy.html
  5. Source: NIH News in Health (NIH): newsinhealth.nih.gov/ issue/ jun2016/ feature2
  6. Source: RDCRN (NCATS/NIH): rarediseasesnetwork.org/ cms/ cegir/ Learn-More/ Glossary
  7. Source: Queensland Health: conditions.health.qld.gov.au/ HealthCondition/ condition/ 4/ 25/ 166/ allergy
  8. Source: MedLinePlus Magazine (NIH): medlineplus.gov/ magazine/ issues/ summer17/ articles/ summer17pg9-10.html
  9. Source: MedLinePlus Magazine (NIH): medlineplus.gov/ magazine/ issues/ spring15/ articles/ spring15pg24-25.html
  10. Source: MedLinePlus Magazine (NIH): medlineplus.gov/ magazine/ issues/ spring13/ articles/ spring13pg22-23.html
  11. Source: MedLinePlus Magazine (NIH): medlineplus.gov/ magazine/ issues/ spring11/ articles/ spring11pg24-25.html
  12. Source: New Zealand Health: health.govt.nz/ your-health/ conditions-and-treatments/ diseases-and-illnesses/ allergies
  13. Source: New Zealand Health: health.govt.nz/ your-health/ conditions-and-treatments/ diseases-and-illnesses
  14. Source: NHS Choices UK: nhs.uk/ conditions/ Allergies/ 
  15. Source: NCI Thesaurus
  16. Source: Human Phenotype Ontology
  17. Source: OAE Ontology
  18. Source: MedLinePlus Magazine (NIH): medlineplus.gov/ magazine/ issues/ spring13/ articles/ spring13pg22-23.html

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.