Have you ever wondered should you use HOT or COLD after a minor injury? While every case is not the same. Here is a general rule of thumb First 72 hours after an injury use COLD. This decreases the blood flow, by a process called vasoconstriction. This results in decreasing the swelling to the area. This is why after a cold pack your skin might appear to have lost some color. The 2 weeks following use 20 minutes of HEAT followed by 20 minutes of COLD After those 2 weeks in most cases you can then use just HEAT. Heat increases blood flow by a process called vasodilation. That’s why after a nice long shower your skin might have a rosy glow.