According to the Mayo Clinic, itching skin inside of a cast can be relieved with an over-the-counter antihistamine. Blowing cool, dry air from a hair dryer under the cast can cause temporary relief. Applying a cold compress to the affected area may also help.
To prevent itching, both the cast and the skin should be kept clean and free of debris, powders, skin lotions, fragrances and other products that may cause irritation. Water should not be allowed to get under the cast, and the cast should always be covered before bathing or taking part in any other activity where the cast may become wet. While it may be tempting to remove padding from within the cast, it should be left intact.
While itching is common, other symptoms of irritation may require medical attention. For example, red and raw looking skin is not normal and should be looked at by a doctor. Burning, stinging, swelling, pain, tightness, a foul odor, and blue, cold, and numb extremities should be addressed immediately. If the limb, fingers or toes become immobile, the patient should seek medical attention immediately.
The Mayo Clinic never recommends sticking an object, such as a coat hanger or knitting needle, under the cast for itching purposes, as they can break the skin, resulting in infection.