When gangrene affects your skin, signs and symptoms may include:

• Skin discoloration — ranging from pale to blue, purple, black, bronze or red, depending on the type of gangrene you have
• Swelling or the formation of blisters filled with fluid on the skin
• A clear line between healthy and damaged skin
• Sudden, severe pain followed by a feeling of numbness
• A foul-smelling discharge leaking from a sore
• Thin, shiny skin, or skin without hair
• Skin that feels cool or cold to the touch

If you have a type of gangrene that affects tissues beneath the surface of your skin, such as gas gangrene or internal gangrene, you may notice that:

• The affected tissue is swollen and very painful
• You're running a low-grade fever and generally feel unwell

A condition called septic shock can occur if a bacterial infection that originated in the gangrenous tissue spreads throughout your body. Signs and symptoms of septic shock include:

• Low blood pressure
• Fever, possibly, though temperature may also run lower than the normal 96.8 F (36 C)
• Rapid heart rate
• Lightheadedness
• Shortness of breath
• Confusion

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.

Several factors increase your risk of developing gangrene. These include:

• Diabetes. If you have diabetes, your body doesn't produce enough of the hormone insulin (which helps your cells take up blood sugar) or is resistant to the effects of insulin. High blood sugar levels can eventually damage blood vessels, decreasing or interrupting blood flow to a part of your body.
• Blood vessel disease. Hardened and narrowed arteries (atherosclerosis) and blood clots also can block blood flow to an area of your body.
• Severe injury or surgery. Any process that causes trauma to your skin and underlying tissue, including an injury or frostbite, increases your risk of developing gangrene, especially if you have an underlying condition that affects blood flow to the injured area.
• Smoking. People who smoke have a higher risk of gangrene.
• Obesity. Obesity often accompanies diabetes and vascular disease, but the stress of extra weight alone can also compress arteries, leading to reduced blood flow and increasing your risk of infection and poor wound healing.
• Immunosuppression. If you have an infection with the human immunodeficiency virus (HIV) or if you're undergoing chemotherapy or radiation therapy, your body's ability to fight off an infection is impaired.
• Medications or drugs that are injected. In rare instances, certain medications and illegal drugs that are injected have been shown to cause infection with bacteria that cause gangrene.

Gangrene can lead to scarring or the need for reconstructive surgery. Sometimes, the amount of tissue death is so extensive that a body part, such as your foot, may need to be removed (amputated).

Gangrene that is infected with bacteria can spread quickly to other organs and may be fatal if left untreated.