Necrotizing cellulitis and necrotizing fasciitis are bacterial soft tissue infections that enter through wounds in the skin.

Cellulitis is a common infection that occurs when bacteria enter the deeper layers of skin and the soft tissue beneath the skin. Without treatment, cellulitis may lead to necrosis, which is the death of bodily tissue in the skin.

Necrotizing fasciitis is a rare and severe bacterial infection that causes necrosis in the connective tissues of the muscles and other tissues and may lead to serious complications and death. It may develop as a complication of cellulitis.

Although necrotizing cellulitis and fasciitis share various similarities, the infections can require different methods of diagnosis.

This article looks at both conditions and their associated symptoms. It also looks at the causes, risk factors, diagnoses, treatments, and outlook for both types of infection.

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Necrotizing cellulitis, which people also call gangrenous cellulitis, is a severe progression of the common skin infection called cellulitis.

Cellulitis typically occurs when bacteria enter the skin through wounds, such as cuts from injuries or insect bites or stings. The infection occurs in the deep layers of the skin and the surrounding tissue.

If a person receives an early diagnosis and treatment for cellulitis, they typically make a complete, fast recovery.

Without treatment, however, cellulitis may spread and progress. The infection may cause necrosis of the skin and the tissue underneath the skin. This involves the irreversible damage and death of cells in the skin and surrounding tissue. Necrosis may spread to the other soft tissues.

Learn more about cellulitis.

Necrotizing fasciitis is a rare bacterial infection that affects the soft tissues and the fascia, a thin lining of connective tissue that surrounds the muscles, blood vessels, and nerves.

Necrotizing means causing the death of cells in the tissue, and fascia refers to inflammation of the fascia.

The infection is severe and spreads rapidly through the body.

Learn more about necrotizing fasciitis.

Types of infection

There are four main types of necrotizing fasciitis. Each type refers to the bacteria that causes the infection.

These types of necrotizing fasciitis are:

  • Type I: More than one type of bacteria causes type I necrotizing fasciitis. The responsible bacteria may include Staphylococcus aureus, Escherichia coli (E. coli), and various other strains. Type I most commonly affects older people and those with diabetes and other conditions.
  • Type II: Methicillin-resistant staphylococcus aureus (MRSA), hemolytic group A streptococcus, or both cause type II necrotizing fasciitis. The infection affects all age groups, and anyone can contract it. People sometimes refer to type II as a flesh-eating disease.
  • Type III: The bacteria Clostridium perfringens typically causes type III necrotizing fasciitis. Type III leads to pockets of gas beneath the skin, which causes a crackling or popping sound called crepitus.
  • Other organisms: Marine organisms may cause another type of necrotizing fasciitis. A person may encounter these by eating raw seafood, seawater entering open wounds, or injury from sea creatures. Infections from marine organisms may be life threatening and require immediate medical attention.

Fungal infections may also lead to necrotizing fasciitis in people with compromised immune systems.

Necrotizing cellulitis and necrotizing fasciitis may present similarly.

Symptoms of necrotizing cellulitis

Symptoms that occur in the skin may include:

  • warmth
  • tenderness
  • severe pain
  • swelling
  • gangrene and necrosis in the skin, which may cause red, purple, or black patches
  • foul-smelling blisters or sores
  • erythema

Erythema refers to changes in skin coloration. Depending on a person’s skin tone, this can appear as red, pink, purple, or a subtle darkening of the existing skin color.

A person may also experience flu-like symptoms, such as:

Symptoms of necrotizing fasciitis

Necrotizing fasciitis spreads rapidly. Symptoms that occur in the skin may include:

  • warmth
  • swelling
  • severe pain
  • erythema
  • black, gray, purple, or black patches
  • bruising
  • blisters, ulcers, and spots
  • infected areas that ooze pus
  • demarcated patches that resemble burn marks
  • crepitus
  • gangrene and necrosis
  • numbness

A person may also experience:

Bacteria entering the body through wounds in the skin cause necrotizing cellulitis and fasciitis. The risk factors for each type of infection and some of the bacteria that cause them differ.

Causes and risks for necrotizing cellulitis

Bacteria from the Staphylococcus and Streptococcus groups most commonly cause cellulitis. They may enter through a wound such as a cut or scrape, insect bite, burn, or surgical incision.

Without treatment, the infection may spread and can result in necrosis of the skin and surrounding soft tissue.

Risk factors include various health conditions, such as:

Other risk factors include:

  • injection drug use
  • older age
  • surgery
  • injury
  • environmental factors, such as unsanitary water

Causes and risks for necrotizing fasciitis

Bacteria entering through wounds in the skin typically cause the infection. A person may also contract the bacteria from direct contact with someone who is carrying it.

The responsible bacteria can include:

  • Streptococcus
  • Staphylococci
  • E. coli
  • Clostridium

Risk factors include various health conditions, such as:

Other risk factors include:

The methods of diagnosis for necrotizing cellulitis and fasciitis may differ. Diagnosis can include a physical exam and laboratory tests, such as blood tests.

Diagnosing necrotizing cellulitis

Doctors often diagnose cellulitis by its appearance.

They may perform a physical examination and ask questions regarding a person’s symptoms and medical history. They may also carefully examine a person’s skin to help determine where the bacteria entered the body.

A doctor will not typically order blood tests or imaging to diagnose cellulitis.

Diagnosing necrotizing fasciitis

To diagnose necrotizing fasciitis, a doctor may carefully examine the site of infection and injury. They may also order laboratory tests, which can include:

The treatment for necrotizing necrotizing cellulitis and fasciitis can include antibiotics, hospitalization, and the surgical removal of necrotic tissue.

Treating necrotizing cellulitis

Treatment for necrotizing cellulitis can involve:

  • antibiotics taken by mouth or intravenously
  • debridement, which is the surgical removal of gangrenous or necrotic skin tissue
  • hospitalization and monitoring

Treating necrotizing fasciitis

Doctors typically begin treatment for necrotizing fasciitis immediately, as the infection spreads rapidly and often leads to severe complications.

Treatment can involve:

  • IV antibiotics
  • hospitalization and monitoring
  • surgeries to remove necrotic tissue
  • blood transfusion

The outlook for necrotizing cellulitis and fasciitis may depend on how early a person receives diagnosis and treatment.

Outlook for necrotizing cellulitis

The outlook for cellulitis is typically positive. However, necrotizing cellulitis may require extensive treatment, including surgery.

If a person does not receive timely treatment, cellulitis can lead to severe complications. These include blood infection, bone tissue infection, sepsis, and necrotizing fascia.

Outlook for necrotizing fasciitis

The outlook for necrotizing fascia is generally poor. Complications of the infection are common and can include organ failure and sepsis.

According to the Centers for Disease Control and Prevention (CDC), even with treatment, 1 in 5 people with the infection died based on 5 years’ worth of data.

Necrotizing cellulitis and fasciitis are bacterial infections that enter through openings in the skin and cause tissue death.

Necrotizing cellulitis affects the deep layers of skin and surrounding tissues, and fasciitis affects the fascia and other deep tissues.

Both infections are severe and can be life threatening. They may present with similar symptoms and require similar treatment. Treatment can include antibiotics and the surgical removal of necrotic tissue.