From Longman Dictionary of Contemporary Englishallergenal‧ler‧gen /ˈælədʒən $ -lər-/ noun [countable] a substance that causes an allergy
Examples from the Corpus
allergen• The antibodies are protein molecules that can fit on to an allergen and inactivate it.• The dust mite, which thrives in warm, moist air, is the greatest source of allergens for asthmatics.• You should also be suspicious of foods that are known to be potent allergens.• Certain foods seem to contain more potent allergens than others.• Half the children received shots designed to provide immunity to seven allergens such as dust mites and pollens.• Antibodies formed in response to the allergens lead to the release of histamine, which is what produces allergic symptoms.• Obviously, avoiding exposure to allergens is the best way to prevent allergic reactions. 