Allergen

n. substance which causes allergies

Most humans mount significant IgE responses only as a defense against parasitic infections. However, some individuals mount an IgE response against common environmental antigens. This hereditory predisposition is called atopy. In atopic individuals, non-parasitic antigens stimulate inappropriate IgE production, leading to type I hypersensitivity. A nonparasitic antigen capable of stimulating a type I hypersensitivity reaction in atopic individuals is called an allergen.
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Noun
1. any substance that can cause an allergy
(hypernym) substance, matter
(hyponym) ragweed pollen

n. allergen, substance which causes allergies

adj. allergenic, causing allergic reactions

noun
substance which produces hypersensitivity
food allergen = substance in food which produces an allergy