Food Allergy -- pecan: A pecan allergy is an adverse reaction by the body's immune system to pecans or food containing pecans. The body's immune system produces immunoglobulin E (IgE - an antibody) and histamine in response to contact with the allergen. The specific symptoms that can result can vary considerably amongst patients from a severe anaphylactic reaction to asthma, abdominal symptoms, eczema or headaches