Zirtek allergy tablets are used to treat people who suffer from hay fever or seasonal allergic rhinitis all year allergies such as dust or pet allergies and treats urticaria which is swelling redness and itchiness of your skin zirtek tablets contain the active ingredient cetirizine dihydrochloride which is an antihistamine which blocks the effects of a substance called histamine which occurs naturally in your body antihistamines relieve the unpleasant symptoms and discomfort such as snee