Desloratadine is in a class of medications called antihistamines. It works by blocking histamine, a substance in the body that causes allergic symptoms. Desloratadine is used in adults and children to relieve hay fever and allergy symptoms, including sneezing, runny nose, and red, itchy, and tearing eyes. It is also used to relieve symptoms of urticaria (hives, red, itchy raised areas of the skin), including itching and rash.