Clarityn contains the active ingredient loratadine, an antihistamine used to treat allergies and relieve the symptoms of hay fever (allergy to pollen, dust, or other substances in the air) and other allergies. When your allergy season starts, take Clarityn a Day for powerful, all-day symptom relief. Clarityn allergy can get you back to feeling normal and free from allergy symptoms with a single daily dose. It also relieves runny noses, sneezing, itchy, watery eyes and an itchy nose or throat.