A blood test will help your doctor tell what you are allergic to and what you need to avoid. If you need to avoid anything at all.
If you are allergic, your symptoms are triggered by normally harmless substances in your local environment. These triggers are called allergens.
It is important that you try to avoid, or at least reduce, exposure to allergens since they add up to cause allergic reactions and may worsen your allergy as well as your condition. In rare occasions, allergens may even cause anaphylactic reaction, which is an emergency situation.