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Updated February 08, 2008

Definition: An allergen is any normally harmless substance that causes a reaction in an allergic person. The immune system of a person with allergies responds to an allergen in much the same way the immune system normally responds to a germ, or antigen.
Pronunciation: AHL-er-jen
Also Known As: allergy trigger
For someone with a dairy allergy, milk is an example of an allergen.
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