Allergy is caused when a person is exposed to an allergen which releases a number of immune system chemicals, such as histamine that results in allergy. There are three type of allergens which are inhaled allergens, ingested allergens and contact allergens. Allergy tests are conducted by trained specialists to identify any reaction caused to an individual due to a particular substance. Allergies can be determined by carrying out examination of the patient in the form of Allergy Skin Testing, Blood Tests, Spirometry (Lung Function Tests), Food Challenges, Medication (Drug) Challenge, Aspirin Desensitization, Patch Testing . Allergy tests involve exposing you to a very small amount of a particular allergen and recording the reaction.