Definition of allergen in US English:



  • A substance that causes an allergic reaction.

    • ‘During allergy seasons, the local news broadcasts usually tell you what allergens are in the air.’
    • ‘Your allergic reaction happens when your body's immune system mistakes the allergen for a harmful invader.’
    • ‘In such an enclosed environment, allergens from one food can spread to another.’
    • ‘It is well known that vacuum cleaner bags capture large particles but can emit allergens that are too small to be collected in the bag.’
    • ‘If allergens in the air are an asthma trigger, pollutants can make the lungs even more sensitive to them.’
    • ‘Wherever possible, the most effective way of treating allergies is to avoid all contact with the allergen causing the reaction.’
    • ‘Future exposure to the same allergens will cause the reaction to happen again.’
    • ‘Avoid things that could make symptoms worse, such as air pollution and allergens.’
    • ‘Once a person is sensitized to an allergen or chemical, he or she may develop asthma.’
    • ‘The goal is to desensitize you to specific allergens and decrease your need for medications.’
    • ‘If you take away the allergens that were driving it initially, the inflammation is likely to continue.’
    • ‘Gradually your body learns to accept the allergen as the harmless substance it is.’
    • ‘Substances that are normally harmless could act as allergens and trigger a reaction in certain people.’
    • ‘Allergies are caused by the body's immune system reacting to allergens as if they were harmful.’
    • ‘The rash usually clears if the allergen is no longer in contact with the skin, but recurs with any slight contact with it again.’
    • ‘Your doctor may take tests to see what allergens are causing the hay fever symptoms.’
    • ‘Eliminate any known allergens such as certain foods, dust, or pet dander from your household.’
    • ‘The next time you're exposed to the allergen, your immune system launches an allergic reaction.’
    • ‘First, allergic reactions are caused by allergens, the three most common ones being dust and mites, pollen and nuts.’
    • ‘Whether your eczema is due to an irritant, such as detergent, or due to an allergen, such as nickel, care and treatment of your skin is the same.’


Early 20th century: blend of allergy and -gen.