(al'ĕr-jĕn )

[aller(gy) + -gen]

Any substance that causes a hypersensitivity reaction or abnormal immune response. Allergens do not stimulate an immune response in everyone, only in those sensitized to them. Common allergens include inhalants (dusts, pollen), foods (wheat, eggs), drugs (aspirin, serum), infectious agents (e.g., bacteria, viruses), contactants (chemicals, animals), and physical agents (heat, cold).

SEE: allergy; antigen; irritation; sensitization; table - Common Allergies and Allergens.

polymerized a.A chemically altered allergen made into a macromolecule, used in immunotherapy to stimulate a blocking antibody response stronger than the allergen’s normal allergic response.