Approximately 50 million Americans suffer from allergies.1 However, most who have allergies are never actually diagnosed. Allergies happen when your body's immune system reacts to substances that won't cause a reaction to most people. The immune system's function is to help your body fight intruders such as parasites, bacteria or viruses. If you're allergic, your immune system reacts toward natural substances the same way it would react toward something harmful. Your immune system "misreads" something that is otherwise harmless.
Allergies are diagnosed with the following methods:
A skin test involves either a gentle prick with a drop of allergen extract on the surface of your arm or an injection of a small amount of allergen extract into the skin. This method may result in mild swelling and a reddening of the skin, which tells the doctor that you have an allergy.
Blood Test (in vitro test):
A blood test can be used on its own to confirm skin test results. If specific antibodies towards one or more allergens are found in the blood, it means that you are allergic and would have an allergic reaction if exposed to those substances.
1. Allergy Facts _ ACAAI Public Website