Cryotherapy is a kind of physical therapy commonly used in hospital dermatology department, which uses low temperature to act on the lesion tissue – skin lesion, causing necrosis and peeling off of the lesion tissue to achieve the purpose of treatment. At present, the refrigerant used in cryotherapy is mainly liquid nitrogen, which is a colorless, odorless and transparent liquid with a temperature of about -196℃. The main mechanism of its treatment is sudden cooling, so that the tissue cells inside and outside the formation of ice crystals, structural damage and lysis; at the same time, low temperature so that cell dehydration, electrolyte concentration, acidity and alkalinity changes, protein denaturation, cell metabolism and death. Methods of liquid nitrogen freezing: cotton swab method, spray method, closed metal freezing head contact method, etc. The cotton swab method is the easiest. Using cotton swabs dipped in liquid nitrogen, quickly placed on the lesion slightly pressurized, to be thawed and repeated several times depending on the situation. The indications for cryotherapy: 1, proliferative skin diseases, such as common warts, flat warts, infectious molluscum contagiosum. 2, hyperkeratotic or nodular skin diseases, such as limited neurodermatitis, lichen planus, skin amyloidosis, nodular itchy rash, etc. 3, benign skin tumors, strawberry hemangioma, soft fibroma, seborrheic keratosis, etc. Foreign reports on certain early malignant skin tumors, such as basal cell carcinoma, squamous cell carcinoma, malignant melanoma, etc. with cryotherapy, but also has very good results. Cryotherapy can be tolerated by both men and women without anesthesia, and there is no discomfort in superficial treatment; in deep treatment, there is varying degrees of pain that may last for several hours. No scar is usually left. What should be noted after cryotherapy: Protect the wound surface, do not break the blisters or scabs by yourself, otherwise it is easy to cause bacterial infection, if the blisters are large, swollen and uncomfortable, you should go to the hospital under aseptic operation to extract the herpes, preserve the herpes surface, and wait for it to fall off naturally. After cryotherapy, local pigment loss is a more common situation, usually within a few months can gradually return to normal. Contraindications to cryotherapy: Severe cold urticaria, cryoglobulinemia, Raynaud’s disease, and a small number of elderly, frail, intolerant to cryotherapy. Patients with diabetes mellitus with impaired blood circulation in the lower extremities, such as cryotherapy in the lower legs and feet, often form chronic ulcers that do not heal, should be used with caution.