The term REACTION TO AN ALLERGEN can be summarized by two crossword solutions: AHCHOO and SNEEZE. An AHCHOO is an informal term for a sneeze, which is a reflexive response to an irritant in the nose. A SNEEZE is a sudden, involuntary expulsion of air from the lungs through the nose and mouth due to irritation in the nasal passages. Both AHCHOO and SNEEZE are common reactions to allergens such as pollen, dust, pet dander, and certain foods.