Gangrene happens when body tissue dies because it loses its blood supply, becomes infected, or both. The underlying cause is almost always one of two things: blocked blood flow that starves tissue of oxygen, or a bacterial infection that destroys tissue directly. Most cases involve the fingers, toes, or feet, and people with diabetes or blood vessel disease face the highest risk.
How Blood Flow Loss Leads to Tissue Death
Every cell in your body needs a constant supply of oxygen-rich blood. When that supply gets cut off or severely reduced, cells begin to die. This is the basic mechanism behind gangrene, and it can happen through several routes. Atherosclerosis, the gradual buildup of fatty deposits inside artery walls, is one of the most common. As arteries narrow over years, blood flow to the extremities slows to a trickle. The tissues farthest from the heart, especially the toes and feet, are the first to suffer.
Skin color changes follow a recognizable pattern as blood flow drops. The area first looks paler than usual, then turns red or reddish. Over time it shifts to brown, then purple, and finally greenish-black. The skin may feel firm, cool, and tender to the touch. Some people experience severe pain in the area, while others lose sensation entirely.
The Role of Diabetes
Diabetes is the single biggest risk factor for gangrene, and the reason comes down to a dangerous combination. High blood sugar damages nerves over time, particularly in the feet. This nerve damage, called neuropathy, erases your ability to feel pressure, pain, and temperature. People with advanced neuropathy can step on a nail, develop a blister, or burn their foot without noticing. Those painless injuries become open doors for infection.
At the same time, diabetes accelerates blood vessel disease. About half of people who develop diabetic foot ulcers also have significant artery disease in their legs. The nerve damage creates wounds; the poor circulation prevents those wounds from healing. Diabetes also causes changes in foot structure, leading to deformities that put abnormal pressure on certain spots, which makes ulcers even more likely. Among patients with diabetes and severe blood vessel disease in the legs, one-year amputation rates range from 15% to 20%, and those rates have been climbing in recent years.
Injuries, Burns, and Frostbite
Trauma is another common path to gangrene, especially when it damages blood vessels. Severe burns destroy skin and the tiny blood vessels beneath it, leaving tissue vulnerable to both oxygen starvation and bacterial invasion. Frostbite works differently but with a similar result: extreme cold causes ice crystals to form inside cells and blood vessels, rupturing them. Once the vessels are destroyed, blood can’t reach the affected tissue even after rewarming.
Crush injuries, deep wounds, and surgical complications can also trigger gangrene by physically severing or compressing blood vessels. Any wound that stays contaminated or doesn’t receive adequate blood flow is at risk.
Dry Gangrene vs. Wet Gangrene
Not all gangrene looks or behaves the same. Dry gangrene develops slowly when blood flow gradually decreases without infection setting in. The affected skin becomes dry, shriveled, and changes color from brown to purplish-blue to black. It’s most common in people with diabetes or atherosclerosis and tends to stay contained to the area where circulation failed.
Wet gangrene is more dangerous. It develops when bacteria infect the dying or dead tissue, often after a burn, frostbite, or injury. The area swells, blisters, and has a wet, sometimes oozing appearance. Because bacteria spread quickly through damaged tissue, wet gangrene can become life-threatening in a short time. It frequently occurs in people with diabetes who injure a toe or foot without realizing it.
Gas Gangrene: A Rapid Emergency
Gas gangrene is a particularly aggressive form caused by certain bacteria that thrive in environments without oxygen, most commonly a species called Clostridium perfringens. These bacteria typically enter through deep wounds, surgical sites, or crush injuries where tissue has been damaged and oxygen is scarce.
Once inside, the bacteria multiply rapidly and release a cocktail of destructive toxins. Some of these toxins dissolve the membranes of muscle cells, red blood cells, and immune cells. Others break down connective tissue like collagen, allowing the infection to tear through tissue layers at alarming speed. One toxin directly damages blood vessels and kills white blood cells, effectively disabling your body’s ability to fight back. As the bacteria consume tissue, they produce gas that accumulates under the skin, creating a crackling sensation when touched. Gas gangrene can become fatal within hours without emergency treatment.
Fournier’s Gangrene
Fournier’s gangrene is a form of necrotizing infection that affects the perineal area (the groin and genital region). It’s caused by multiple types of bacteria, both those that need oxygen and those that don’t, working together to destroy tissue. The bacteria most commonly involved are the same ones that normally live in the perineal and genital area, including E. coli and Staphylococcus aureus. Fungal infections can also play a role.
This form carries high mortality, with sepsis and organ failure responsible for the majority of deaths. Patients with diabetes, heart disease, or kidney disease face significantly worse outcomes. Aggressive surgical removal of dead tissue can reduce mortality to around 16%, making early recognition critical.
Other Risk Factors
Beyond diabetes and trauma, several other conditions raise your risk:
- Peripheral artery disease narrows blood vessels in the legs and feet, reducing blood flow to extremities even without diabetes.
- Smoking damages blood vessel walls and accelerates atherosclerosis.
- Immune suppression from conditions like HIV or medications like chemotherapy makes it harder to fight infections before they spread.
- Obesity compresses blood vessels and is linked to both diabetes and poor wound healing.
- Raynaud’s disease causes small arteries in the fingers and toes to spasm and temporarily shut down blood flow, which in severe cases can lead to tissue damage.
How Gangrene Is Treated
Treatment depends on the type and severity, but surgery is almost always involved. The primary goal is removing all dead and infected tissue, a process called debridement. For wet or gas gangrene, this surgery is urgent and may need to be repeated multiple times. If the gangrene has destroyed too much tissue in a limb, amputation may be the only option to prevent the infection from spreading further.
Antibiotics are given alongside surgery to fight bacterial infection. Because gangrene infections typically involve multiple types of bacteria, broad-spectrum antibiotics covering a wide range of organisms are used from the start, then adjusted as lab results identify the specific bacteria involved.
Hyperbaric oxygen therapy, which involves breathing pure oxygen in a pressurized chamber, is sometimes used as an additional treatment. A meta-analysis of thirteen studies found that patients with Fournier’s gangrene who received hyperbaric oxygen had significantly lower death rates compared to those treated without it. However, it didn’t consistently reduce the number of surgeries needed or shorten hospital stays. It’s considered a supplement to surgery, not a replacement.
Recognizing the Warning Signs
Gangrene progresses through visible stages. Early on, the skin in the affected area looks unusually pale. It then shifts to red, followed by brown, and eventually purple or greenish-black. The skin may feel cool and firm. Pain can be intense at first, then suddenly disappear as the nerves in the area die, which is a particularly dangerous sign because the lack of pain can make you think the problem is improving.
Wet and gas gangrene add additional red flags: swelling, blistering, a foul-smelling discharge, and fever. With gas gangrene, you may feel a crackling sensation under the skin from trapped gas. Any wound that develops these features, especially with spreading redness and fever, needs emergency medical attention. The difference between early and late treatment in gas gangrene or Fournier’s gangrene can be the difference between a surgical procedure and a fatality.