Allergic Conditions Make an Appointment Refer a Patient Ask a Question Reviewed by Henry Milgrom, MD (February 01, 2017) Allergic conditions and allergic reactions occur when the immune system misidentifies harmless foreign substances-called allergens-and reacts to them as if they were harmful. Learn about common allergens such as food and insect stings. These allergens can cause different types of allergies and related conditions that affect different parts of the body. In this section, learn about the most common allergic conditions and what types of allergens typically cause them. Types Allergic conditions include: Allergic Asthma Anaphylaxis Hives (Urticaria) Rhinitis (Nasal Inflammation) Eczema (Atopic Dermatitis) View Allergy Home Allergens Allergy Diagnosis Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.