Fifteen to 20 minutes has been shown to be the most effective time to use ice for an acute injury. Ice should not be placed on an injury for longer than 20 minutes, in order to prevent frostbite or other negative side effects.
This answer provided for NATA by the Eastern Kentucky University Athletic Training Education Program.
You should ice an injury for 48 hours after it occurs because of the swelling (and for the sympathy you might get, of course). While swelling indicates an increased fluid or blood deposits in the area, it slows down recovery from the injury as the swelling from fluid makes joints stiffer and more painful, which in turn makes them weaker. Ice reduces the swelling-and pain.
After that 48-hour period, you use ice to generate heat (when you take the ice away it heats up) or heat alone on the injury to warm it up. The heat loosens up the joint or muscle, giving you more flexibility and allowing you to move it more freely during rehabilitation.
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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.