Ice therapy or cryotherapy is often thought of as the therapy of choice for acute injuries. Actually, the application of ice over any painful tissue is usually effective at any stage of an injury. It works by constricting blood flow to the tissue, thereby reducing swelling, pain, and muscular spasms. It is very important to use ice correctly. It should be used for a maximum of 20 minutes, but may be applied each hour. Also, it is important that you do not apply the ice directly to the skin. Instead, wrap the ice pack in a paper towel or thin damp cloth prior to applying to the injured area.