Why do people get gangrene?

Several reasons: Gangrene is tissue death. Generally the cause is due to poor or disrupted blood supply due to cardiovascular disease (hardening of the arteries) or infection. Blood clots are also a cause. Gangrene can also be caused by external sources such as severe burns, both chemical and thermal (heat and cold (frostbite)). Certain conditions like diabetes, kidney failure, high cholesterol will increase risk.

Poor circ&infection: It is usually due to a combination of compromised arterial circulation followed by secondary bacterial infection.