The difference between gangrene and necrosis is commonly seen as follows: 1. Different definitions: gangrene is an alteration of a special form of tissue necrosis that becomes black or dark green as a result of infection secondary to putrefactive bacteria or the influence of other factors. The necrotic tissue is decomposed by putrefactive bacteria to produce hydrogen sulphide, which combines with iron decomposed from haemoglobin to form iron sulphide, thus making the necrotic tissue black. Necrosis is a type of cellular damage caused by premature cell death, a localized tissue cell death in the living body characterized by changes in enzyme solubility. Necrosis is a life-threatening disease that occurs when a large amount of healthy tissue dies and is one of the clinical manifestations of necrosis. Necrosis involves the cellular level, whereas gangrene involves the tissue level; 2. The pathogenesis is different: the cellular characteristics of death caused by necrosis are due to the loss of integrity of the cell membrane and swelling of the cells. Necrosis is caused by insufficient blood supply, which may be due to ischemic causes or infections; 3. Different classifications: Necrosis can be coagulative necrosis, liquefactive necrosis, caseous necrosis and adipose necrosis, and fibrinoid necrosis, respectively. Gangrene is divided into dry gangrene, wet gangrene, gas gangrene and necrotizing fasciitis.