Cryotherapy is a treatment method that uses the physical properties of refrigeration substances to act on the lesion tissue at low temperature to reduce the local lesion tissue skin temperature, capillary constriction, tissue cell necrosis, to remove warts or septic granuloma, etc. Cryotherapy is usually applied to all kinds of benign skin diseases or malignant skin tumors and precancerous lesions, freezing agents including liquid nitrogen and dry ice, usually using liquid nitrogen, because the refrigeration temperature is lower, more convenient and safe to use. Clinically, the following three treatment modalities are mainly adopted: 1. Cotton swab method: applicable to smaller superficial damage, using cotton swabs dipped in liquid nitrogen to directly contact the lesions, gently point pressure to make local edema or repeated deep points, pressure until frozen hard and white. Patients feel tingling at the freezing site during treatment, but it is generally tolerable. At the end of the treatment, the skin tissue is frozen and white, and after a few minutes, local thawing and swelling, pain, and erythema and blisters appear within 1-2 days. Generally within 1-2 weeks, the scab can be self-healing, with local temporary hyperpigmentation or hypopigmentation; 2. Spray method: Applicable to large area, surface unevenness and tumors and other deep lesions, can also be used for the treatment of oral damage. Liquid nitrogen is evaporated in the treatment device to generate pressure, which is sprayed out from the nozzle and sprayed on the skin lesion to achieve the treatment purpose; 3, closed contact treatment: applicable to the treatment of deeper skin lesions. A special treatment machine is required. Liquid nitrogen is sprayed on the freezing head through the catheter and placed on the lesions after cooling. In this method, liquid nitrogen can be continuously sprayed on the freezing head to maintain low temperature. After cryotherapy, the trauma should be kept clean and dry, such as the occurrence of blisters, blood blisters and peeling is a normal phenomenon after cryotherapy, and can generally subside on its own. If the blister is too large, a sterile syringe can be used to puncture the wall of the blister and release the herpes, but care should be taken that the wall remains attached to the skin surface to reduce the chance of secondary infection. If the condition requires repeat treatment, this should be done after the scab has fallen off.