Liquid nitrogen is a chemical that is super cold, about -200 degrees Celsius.
Liquid nitrogen will instantly freeze anything it touches. It is used to kill cells that make up diseased or cancerous tissue. Tissue that has been frozen dries out and falls off.
Habif TP. Dermatologic surgical procedures. In: Habif TP, ed. Clinical Dermatology. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 27.