Causes of Gangrene
Gangrene may occur due to one or some of the following causes:

Lack of blood supply. Your blood provides oxygen, nutrients to feed your cells, and immune system components, such as antibodies, to ward off infections. Without a proper blood supply, cells can't survive, and your tissue decays.

Infection. If bacteria thrive unchecked for long, infection can take over and cause your tissue to die, causing gangrene.

Trauma. Wounds that are traumatic, such as gunshot wounds or crushing injuries from car crashes, can cause bacteria to invade tissues deep within the body. When such tissues are infected, gangrene can occur.

Types of gangrene
Dry gangrene. Dry gangrene is characterized by dry and shriveled skin ranging in color from brown to purplish blue or black. Dry gangrene may develop slowly. It occurs most commonly in people who have arterial blood vessel disease, such as atherosclerosis, or in people who have diabetes.
Wet gangrene. Gangrene is referred to as "wet" if there's a bacterial infection in the affected tissue. Swelling, blistering and a wet appearance are common features of wet gangrene.

It may develop after a severe burn, frostbite or injury. It often occurs in people with diabetes who unknowingly injure a toe or foot. Wet gangrene needs to be treated immediately because it spreads quickly and can be fatal.

Gas gangrene. Gas gangrene typically affects deep muscle tissue. If you have gas gangrene, the surface of your skin may initially appear normal.

As the condition progresses, your skin may become pale and then evolve to a gray or purplish red color. A bubbly appearance to your skin may become apparent, and the affected skin may make a crackling sound when you press on it because of the gas within the tissue.

Gas gangrene is most commonly caused by infection with the bacterium Clostridium perfringens, which develops in an injury or surgical wound that's depleted of blood supply. The bacterial infection produces toxins that release gas - hence the name "gas" gangrene - and cause tissue death. Like wet gangrene, gas gangrene can be life-threatening.

Internal gangrene. Gangrene that affects one or more of your organs, such as your intestines, gallbladder or appendix, is called internal gangrene. This type of gangrene occurs when blood flow to an internal organ is blocked - for example, when your intestines bulge through a weakened area of muscle in your abdomen (hernia) and become twisted.

Internal gangrene may cause fever and severe pain. Left untreated, internal gangrene can be fatal.

Fournier's gangrene. Fournier's gangrene involves the genital organs. Men are more often affected, but women can develop this type of gangrene as well. Fournier's gangrene usually arises due to an infection in the genital area or urinary tract and causes genital pain, tenderness, redness and swelling.
Progressive bacterial synergistic gangrene (Meleney's gangrene). This rare type of gangrene typically occurs after an operation, with painful skin lesions developing one to two weeks after surgery.