As a general rule of thumb, you need to ice an injury over 24 to 27 hours. During this time, you can apply cold packs for periods of up to 20 minutes every two to four hours.  Once your skin starts to feel numb, it’s time to remove the pack and give a break to the body. While doing so, make sure you are not applying ice directly on your skin, or you might feel burnt. Also, you should never use a cold compress in a significant injury and avoid applying for long hours.