Allergy

In this Article

• What does an allergy mean?
• What causes allergies?
• Who is at risk and why?
• What are common allergic conditions and their 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
• Allergy At A Glance
• Pictures of Common Allergy Triggers - Slideshow
• Pictures of Pets and Allergies - Slideshow
• Pictures of Home Allegy - Slideshow
• Patient Discussions: Allergies - Describe Your Experience

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

Allergies - Describe Your Experience

The MedicineNet physician editors ask:

Please describe your experience with allergies.

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