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, so that the lesion tissue necrosis and peel off, in order 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. There are several 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, etc. 2, hyperkeratotic or nodular skin diseases, such as limited neurodermatitis, nodular itchy rash, etc. 3, benign skin tumors, such as seborrheic keratosis, soft fibroids, etc. Cryotherapy can be tolerated by both men and women, without anesthesia, shallow treatment without discomfort, deep treatment can have varying degrees of pain and may last for several hours, 1 hour after treatment, the affected area begins to edema, a few will also appear blisters or blood blisters, about 1-2 weeks crust, scabs fall off, the lesion tissue is removed. No scar is usually left. Precautions after cryotherapy: 1. 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, painful and uncomfortable, you should go to the hospital under aseptic operation to extract the herpes, preserve the herpes surface, and wait for its natural fall off. 2, after cryotherapy, local pigment loss is a more common situation, generally within a few months can gradually return to normal. Contraindications to cryotherapy: 1, severe cold urticaria, cryoglobulinemia, Raynaud’s disease, and a few elderly, frail, intolerant to cryotherapy. 2, diabetes mellitus with lower extremity blood circulation disorders, such as in the calf, foot cryotherapy, often the formation of chronic ulcers that do not heal, should be used with caution cryotherapy.