Allergies create inflammation in the airways.  The inflammation causes the release of histamines, chemicals that cause swelling, an excess of mucous secretion, and muscle contractions in the airway.  This is an asthma attack.  (For more information about asthma attacks, go to the Asthma home page.) 

An allergy means your body reacts abnormally to certain substances, called "allergens," that you're sensitive to.  Allergies are specific to an individual, that is, each person "with allergies" reacts only to certain specific allergens, and the symptoms that result, known as the "allergic reaction," are also specific to that person.   The tendency to develop allergies is inherited, but specific allergies are not. 

Many people with allergies also have or develop asthma.  In fact, allergens are one class of asthma triggers – substances that provoke asthma symptoms and asthma attacks. (For more information about asthma triggers, go to Key Point 1.)

There are several types of allergens, including:

• Certain foods, such as fish, shellfish, peanuts, milk, eggs, soy, wheat, and tree nuts
• Certain medicines, such as penicillin, aspirin or other non-steroidal anti-inflammatory drugs such as ibuprofen, and beta-blockers (used to treat heart disease, high blood pressure, and migraine headaches)
• The venom from stinging insects
• Natural rubber latex

But the most common type of allergens that act as asthma triggers are inhaled (breathed in) allergens, including:

• Dust mites (found in ordinary house dust)
• Pollen from flowers, plants, grass, trees, etc.
• Mold (indoor and outdoor)
• Animal dander (from the skin, hair, or feathers of animals)
• Cockroach droppings

If you inhale something you're allergic to, your body produces chemicals called histamines that cause you to have an allergic reaction.  The type of reaction depends on the individual, the specific allergen, and the severity of the allergy. Typical allergic reactions to inhaled allergens include:

• Itchy eyes, nose, or throat
• Watery eyes
• Chest congestion
• Nasal congestion
• Runny nose
• Sneezing
• Wheezing
• Swelling
• Redness

These symptoms can be produced by several allergies, including one of the most common, popularly known as "hay fever," technically known as allergic rhinitis.  According to the American Academy of Allergy Asthma & Immunology, up to 78% of people with asthma also have allergic rhinitis; therefore it is considered a risk factor in developing asthma. (A risk factor is something that increases your chances of getting a particular disease.) 

Because allergens are one class of asthma triggers and so many people with allergies also have asthma, allergy tests are given when you're being examined for asthma.  Allergy tests determine if you have allergies, and what your allergens are.

There are several forms of allergy tests, but the most common pricks your skin with a tiny needle to expose your blood or skin to a tiny amount of a common allergen.  Usually you're pricked in several places at once, each place with a different allergen.  If you're allergic to an allergen, the skin that was exposed to it will show a reaction (such as redness or swelling).  The reactions happen fairly quickly, so you normally have the results within fifteen minutes of the test.

Knowing if you have allergies and what they are is important information for diagnosing and treating asthma.  The treatment you receive will depend, in part, on the nature of your allergies.  For information about treating asthma, go to Key Point 3.