Unless your cast is waterproof, keeping it dry is very important. Your doctor may instruct you to cover it with a plastic bag while you shower, or you can get a specially designed waterproof sleeve. Depending upon where your cast is, you may have to take a sponge bath, which just means that you use a wet sponge or cloth to clean yourself instead of actually getting your whole body wet in the tub or shower. If a plaster cast gets wet, it may lose its strength and no longer be able to keep the injured area still. The cotton padding beneath is hard to dry and may cause your skin to develop a rash or infection.
Doctors sometimes make tiny cuts in the side of a cast to allow room for possible swelling.
Your cast may also develop cracks on its own if it's been hit or crushed, has a weak spot, or if your skin begins to swell underneath. New cracks should be reported to a parent immediately and then examined by your doctor. Also, if you notice that your cast is causing your fingers or toes to turn purple or blue, it may be too tight and your doctor may have to change it. Doctors use a special saw with a dull, round blade that vibrates up and down. The vibration is strong enough to break apart the fiberglass or plaster, but it can't hurt your skin.