Never put anything inside to scratch the skin. Never put creams or powders in the cast to try to help the itching.One thing you can do safely: use a hair dryer on the "cool" setting to blow air into the cast. This often provides relief.  –The StayWell Company, LLC via Nationwide Children's HospitalCastCooler is a device said to relieve odor, itch and skin rash by keeping cast linings dry. For information and to purchase.