Clarityn Allergy is different from many other UK antihistamine brands. This is because Clarityn contains the active ingredient loratadine, whereas some other brands may contain cetirizine or acrivastine. Loratadine is 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. This ingredient works by blocking the action of histamine, which is a chemical naturally produced by the human body. When your allergy season starts, take a 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. Relieves runny nose, sneezing, itchy watery eyes and itchy nose or throat.