Fexofenadine is an antihistamine. It is used to relieve the symptoms of hay fever (seasonal allergic rhinitis) and hives of the skin (chronic idiopathic urticaria) .Antihistamines work by preventing the effects of a substance called histamine, which is produced by the body. Histamine can cause itching, sneezing, runny nose, and watery eyes. Also, in some people histamine can close up the bronchial tubes (air passages of the lungs) and make breathing difficult. Histamine can also cause some people to have hives, with severe itching of the skin.