Cetirizine Dihydrochloride is a second-generation antihistamine used to treat allergic reactions such as hay fever, allergic rhinitis, and urticaria (hives). It works by inhibiting histamine, a substance that is produced during allergic reactions, preventing the common symptoms like sneezing, itching, runny nose, and watery eyes. Cetirizine is known for its effectiveness in treating allergies while causing less sedation compared to first-generation antihistamines.