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Medical Author:

Alan Szeftel, MD

Alan Szeftel, MD

Dr. Szeftel received his Medical Degree from the University of Cape Town Medical School in South Africa. His clinical training was at Groote Schuur Hospital. He completed his Internal Medicine residency at Brigham & Women's Hospital and Harvard University. He is board certified in Internal Medicine, Pulmonary Diseases, Critical Care and Allergy and Immunology.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• Allergy facts
• What does an allergy mean?
• What causes allergies?
• Who is at risk and why?
• What are common allergic conditions, and what are allergy symptoms and signs?
• Hay Fever
• Asthma
• Allergic Eyes
• Allergic Eczema
• Hives
• Allergic Shock
• Where are allergens? Everywhere
• In the air we breathe
• In what we ingest
• Touching our skin
• Injected into our body
• Common Allergy Triggers Slideshow
• Take the Quiz on Allergies
• Allergy Proof Your Home Slideshow
• Find a local Asthma & Allergy Specialist in your town

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 (for example, cat), the substance itself (cat dander), or the specific proteins that provoke the immune response (for example, 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