Recognizing invader
An allergy occurs when the immune system reacts to substances (allergens) that are generally harmless and in most people do not cause an immune response. Antibodies are formed by the immune system in response to the presence of an antigen such as pollen, mold, dust or dander.
Review Date: 07/21/2009
Reviewed By: A.D.A.M. Editorial Team: David Zieve, MD, MHA, Greg Juhn, MTPW,
David R. Eltz. Previously reviewed by Stuart I. Henochowicz, MD,
FACP, Associate Clinical Professor of Medicine, Division of
Allergy, Immunology, and Rheumatology, Georgetown University
Medical School (5/25/2009).
