allergen
An allergen is a mischievous collective of microscopic troublemakers that delight in teasing an otherwise peaceful immune system. Allow their invasion and the body hosts an impromptu fireworks display of tears, itching, and sneezes, free of charge. Ironically troublesome to those seeking health, yet medical science captures them with enthusiasm, cataloging them as prized research specimens. Ultimately consigned to the realm of 'nature's pranks,' they are subdued by the artillery of antihistamines.