I have an ankle sprain, why shouldn't heat be used? my foot is freezing and want to warm it up but wasn't sure why heat packs can't be used?

Ice reduces swelling: Initially after an injury the tissues begin to swell, This can cause pain and stiffness. In the first stages after the injury ice is the best way to reduce that swelling

Ice 24hrs, then heat: Ice is good for the first 24 hours to relieve acute inflammation and swelling. After that, heat will increase circulation and healing. Hope you got an x-ray to be sure its not broken.

Increases swelling: Applying heat too soon after an ankle sprain can increase the swelling of the ankle beyond what would normally occur if heat was not used. Ice, however, will help reduce swelling from an ankle sprain when used shortly after it occurs.