Both heat and ice will help reduce body pain, but there are certain types of injuries for which each should be used, such as muscle injuries.
Ice
Ice should be used for acute pain or to treat new injury that is causing swelling and inflammation. Ice treatment may be used in both the immediate treatment of soft tissue injuries and in later rehabilitation. These effects help prevent the area from becoming stiff, by reducing excess tissue fluid that gathers as a result of injury.
Heat
Heat is an effective and safe treatment for most aches and pains. It causes the blood vessels to dilate which brings more blood into the injured area to stimulate healing of damaged tissues. It has a direct soothing effect.