How do allergists find what I'm allergic to?

With easy tests and. First the allergist takes a complete history of your symptoms and then examines you. Depending on what they find, a simple scratch test is done for specific substances, which might be causing your allergies. Sometimes they may also do a blood test.
Skin/blood tests. 1. Introduce small quantity of allergen into skin, wait for 20 minutes and look for small swelling, redness and itching. 2. Send a blood sample to lab and measure ig. E antibody levels to specific allergens.