Necrosis refers to the localized death of cells or tissues through injury, disease, or the interruption of blood supply. Necrosis is more of a general term for tissue death. The entire process of cell or tissue necrosis is irreversible. Gangrene, on the other hand, refers to the death of cells or tissue caused by the lack of blood supply.
Symptoms of gangrene include a change in skin color, pain, numbness, and swelling. Necrosis and gangrene have much in common in that they refer to the death of tissues, but the major difference is the cause of cell death. As defined above, necrosis is caused by disease and injury, while gangrene is caused by the interrupted blood supply.