Cetirizine is a second-generation antihistamine commonly used to treat allergic reactions such as urticaria, itching, sneezing, and allergic rhinitis. It works by blocking histamine H1 receptors, helping reduce allergy symptoms without significant sedation in most patients. Cetirizine has a relatively fast onset of action and is effective for both acute and chronic allergic conditions. It is generally well tolerated, though some people may experience mild drowsiness or dry mouth. Because it is non-sedating compared with older antihistamines, it is often preferred for daytime use.