Short-Term Effects
Ice packs have certain immediate effects against pain. They numb the surrounding area, making it close to impossible for you to feel pain. In addition, they keep muscles from contracting in painful spasms. If you're experiencing bleeding, ice packs can stop or reduce blood flow by constricting nearby blood vessels. Even if you're not experiencing bleeding, using ice can reduce swelling and bruising from injured blood vessels.
Long-term Effects
When you're injured, your body responds by swelling and inflaming the afflicted area, with resulting pain and redness. Applying ice to the injury stops your body from continuing to swell, reducing the chances of future inflammation. Ice also slows down the cellular process in the body, which sounds sinister but actually helps stop cell damage from spreading.
Risks
There are certain drawbacks to using ice packs. The skin can become so numb that frostbite can develop without you noticing. If body tissue becomes too cold, the body may actually reopen blood vessels in the injured area to warm it up, reversing all the anti-bleeding and other positive effects of vessel constriction. For these reasons, it's best not to use ice packs for more than 10 minutes at one time. You should also wrap a towel around the ice pack before you use it, both to keep your skin from overcooling and to catch any drips.
