What is an Allergen?

An allergen is something that causes allergies. An allergic person's immune system mistakenly thinks the allergen is harmful, so it reacts and causes "allergy" symptoms. Someone who doesn't have allergies can be exposed to the exact same substance -- like pet dander, for example – and not have any symptoms at all.

Allergens are often referred to as "triggers" for allergy and asthma, because they "set off" allergic reactions. There are different types of allergens, and a variety of allergic conditions that they can cause.

About Airborne Allergens

Many common allergens begin as "airborne allergens." They float through the air and can be breathed in, causing symptoms. These airborne allergens land on surfaces, too, and cause an allergic reaction when an allergic person comes in contact with them.

Common allergens are:

• Dust mite debris
• Mold allergens
• Pet dander
• Pollen particles/allergens

Sometimes these allergens are called "indoor/outdoor" allergies because they occur in your environment – say, when the pollen count is high during pollen season or when there are dust mites on indoor surfaces.