When you are exposed to allergy triggers, your body produces inflammatory substances, such as histamine, which may cause symptoms like nasal congestion, sneezing, and itchy, watery eyes. Most over-the-counter allergy pills only block 1 allergic substance. FLONASE SENSIMIST helps block 6 key inflammatory substances,* including histamine, prostaglandins, cytokines, tryptases, chemokines and leukotrienes.