An allergen is a substance that can cause an allergic reaction. In some people, the immune system thinks allergens are foreign or dangerous. This is what leads to allergy symptoms.
Common allergens include:
Animal proteins and animal dander
Bacteria and viruses
Drugs (such as antibiotics or medications you put on your skin)
Foods (such as milk, chocolate, strawberries, wheat)
Wasserman SI. Approach to the patient with allergic or immunologic disease. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 257.
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.