First of all, we should clarify the principle of liquid nitrogen freezing, liquid nitrogen freezing is a very low temperature gas, nitrogen cryogenic conditions can become liquid, and contact with the skin caused by the obvious cooling of the tissue, resulting in crystalline necrosis, crusting off, this process takes time generally 2-3 weeks or 3-4 weeks, because the liquid nitrogen freezing treatment after the release of a large amount of heat from the tissue will form crystals and then edema. When the crystalline edema necrosis begins, swelling of the frozen skin area will be observed, and blood blisters will appear when the reaction is severe, and pain will be more obvious at this time. Most patients will experience edema, blood blisters, and painful reactions for about a week after liquid nitrogen freezing before crusting over and peeling off naturally. The process usually takes 2-3 weeks. If it takes more than 3-4 weeks, the scab will not come off to the hospital. If there is no response after 1-2 weeks of freezing, it means that the effect is not enough and needs to be re-frozen.