An allergist is a doctor who diagnoses and treats allergies, asthma and immunologic conditions. In addition to medical school and residency, allergists have two to three years of special training in allergy and immunology. Allergists can help you manage your allergies or asthma and avoid serious reactions. An allergist  is a doctor who specializes in certain conditions that affect your immune system. Your immune system is made up of special cells, organs and tissues that fight off disease.