An Allergist deals with a person's reactions to outside stimulus. For example, someone might have an allergy to peanuts, or ragweed. An allergist deals with the symptoms of allergies.and how to control those symptoms.
An Immunologist on the other hand deals with a person's internal ability to protect itself from disease. It deals with the immune system itself. Most people who are Allergists are also Immunologists as the fields are closely related to each other

