Cold compresses do not reduce swelling, but choosing the right time to apply cold compresses can prevent swelling, and can prevent further aggravation of swelling. In general, cold compress can be applied within 24 hours after trauma, and the earlier the cold compress is applied, the better the effect is. The cold compress can lower the local skin temperature, constrict the subcutaneous blood vessels, reduce the exudation and edema of tissue cells, reduce the damage and bleeding of capillaries, prevent swelling in the early stage, and prevent the swelling that has already appeared from continuing to aggravate, which is helpful for the recovery of trauma. However, cold compress also has certain requirements, the temperature should not be too low and the time of cold compress should not be too long, so as not to cause frostbite of the skin or make the blood vessels contract for a long time, resulting in local tissue ischemia and hypoxia. If there is a wound on the skin after trauma, it is important to protect the wound when applying cold compresses to prevent contamination of the wound causing infection.