There are a wide variety of conditions that can result in itching and scratching.  These can include, but are not limited to, allergies, fleas, mange mites, food allergies, sensitivities to environmental factors, metabolic disorders and skin infections.  The most common cause of constant itching is pollen allergy.  Your pet may experience seasonal allergies.  Visit your veterinarian to determine the cause of itching, there are many treatments he/she can administer that may dramatically help your pet.