Azelastine works by blocking the H1 receptors on cells, which are receptors that are normally activated by the chemical histamine. When the body is exposed to an allergen, immune cells (called mast cells and basophils) release histamine. Since azelastine blocks histamine from activating the H1 receptors, the symptoms that are typically caused by histamine are lessened. Azelastine also has anti-inflammatory effects and reduces congestion.