Gangrene is a term used to describe a number of conditions in which tissue becomes necrotic and decays. Most often, gangrene occurs in the extremities of the body, such as the feet or hands, though on occasion, such necrosis may be found elsewhere. Once gangrene has passed a certain point, amputation of the affected extremities is often the only solution, though medical technology has become better at solving the problem with less drastic actions. There are four major types of gangrene: wet gangrene, dry gangrene, gas gangrene, and internal gangrene. Of these, internal gangrene is relatively rare and is often not listed as a type of gangrene, gas gangrene is a special type of bacterial gangrene that is sometimes simply classified as wet gangrene, and dry and wet gangrene are the two major forms.

Dry gangrene occurs when blood cannot reach a part of the body, so that the tissue is no longer fed. Dry gangrene may occur for a number of reasons, such as a blood clot or insufficient circulation. Diabetics are particularly susceptible to dry gangrene, as they often have impaired circulation. The condition sometimes referred to as diabetics foot can, in the worst case, lead to severe gangrene that may require ultimate amputation of the extremity. Dry gangrene progresses more slowly than wet gangrene, and if caught early on, it may be reversed through surgery before the tissue becomes necrotic.

Wet gangrene may be caused by an abrupt cessation of blood flow to an area and a subsequent infection. This may be the result of severe cold, heat, or a serious injury. The classic image most people have of gangrene comes from old Western movies or war films in which someone is shot and the untreated wound becomes infected and eventually turns necrotic. Once the flesh has become necrotic, it must be removed from the body before the necrosis spreads, either through specific surgery or total amputation. In the past, maggots were sometimes used to devour the necrotic flesh, and while this practice was frowned upon for a period of time, it is beginning to see a resurgence in many quarters.

Gas gangrene is a specific type of wet gangrene caused by a bacterial infection and the subsequent release of gas inside the tissue. The most common bacteria responsible for gas gangrene is Clostridium perfringens, which make their way into the body from the surrounding environment through open wounds. Gas gangrene progresses extremely rapidly and is nearly always an emergency situation. Sometimes, antibiotics may be used in the early stages to fight off the bacteria, at which point surgery can be used to remove the small pockets of necrotic flesh if the condition was caught early enough.

Internal gangrene is the rarest type of gangrene, in which blood circulation is impeded to various internal organs. Most often, internal gangrene occurs in the appendix, gallbladder, or intestines, and it can be extremely painful and dangerous. If the condition is caught early on, surgery or medication is usually undertaken to remove the impediment to blood circulation. In later stages, more extensive surgery may be necessary.