The three most common triggers of allergy are dust mites, grass pollen and cats. More than 9 out of 10 people with allergies are sensitive to at least one of these. To determine which specific substances are triggering your allergies, your allergist/immunologist can test your skin or your blood by using tiny amounts of commonly troublesome allergens. As a general rule, inhaled allergens such as dust mites, tree, grass or weed pollens will produce respiratory symptoms and ingested (food) allergies will produce skin and/or gastrointestinal symptoms or anaphylaxis. However, both types of allergens (ingested and inhaled) can produce the full spectrum of allergy symptoms.

In order to deal with allergy symptoms most effectively it is first necessary to determine what is causing your allergy. For instance, you don't have to get rid of your cat if you are allergic to dust mites but not cats.

Function

• Waste products from dust mites (tiny bugs you can't see, that live in your home);
• Proteins from furry pets, which are found in their skin secretions (dander), saliva and urine (it's actually not their hair);
• Molds in your home or in the air outside;
• Tree, grass and weed pollen;
• Cockroach droppings.

• Venoms from the stings of bees, wasps, yellow jackets, fire ants and other stinging insects;
• Foods, such as nuts;
• Natural rubber latex, such as gloves or balloons;
• Drugs, such as penicillin.

• Prick Technique
  A small amount of allergen is introduced into the skin by making a small puncture through a drop of the allergen extract. If an allergy is present, this test will cause a chain reaction to begin in your body.
  
  People with allergies have an allergic antibody called IgE (immunoglobulin E) in their body. Upon encountering an allergen, IgE activates special cells called mast cells, which in turn release chemicals called mediators -- such as histamine, the chemical that causes redness and swelling. This localised swelling occurs only in the spots where the tiny amount of allergen was introduced as part of the test. Test results are available within 15 minutes, and any swelling goes away within 30 minutes.
   
• Intradermal
  A small amount of allergen is injected under the skin with a syringe. This form of testing is more sensitive than the prick skin test method and may be used if the prick skin tests are negative.
   
• Scratch Tests
  Not commonly used at the present, this technique involves abrading the skin and then dropping the allergen on the abraded site.
   
• Challenge Testing
  Small amounts of the suspected allergen are introduced by oral, inhaled or other routes. With the exception of food and medication, challenges are rarely performed. When they are performed, the must be closely supervised by an allergist/immunologist.
   
• Blood (RAST) Test
  The RAST (radioallergosorbent) test is a blood test that involves drawing blood, and is generally used only in cases where skin tests can not be performed, such as patients taking certain medications or those with skin conditions that may interfere with skin testing. It costs more, and the results are not available as rapidly as with skin tests.