Phlegmon is a medical term describing an inflammation of soft tissue that spreads under the skin or inside the body. It’s usually caused by an infection and produces pus. The name phlegmon comes from the Greek word phlegmone, meaning inflammation or swelling.

Phlegmon can affect internal organs such as your tonsils or appendix, or can be under your skin, anywhere from your fingers to your feet. Phlegmon can spread rapidly. In some cases, phlegmon can be life-threatening.

The difference between phlegmon and abscess is as follows:

  • A phlegmon is unbounded and can keep spreading out along connective tissue and muscle fiber.
  • An abscess is walled in and confined to the area of infection.

Abscess and phlegmon may be difficult to distinguish in some cases. Sometimes, phlegmon results when the infected material inside an abscess breaks out of its self-containment and spreads.

Usually, an abscess can be drained of its infected fluid. A phlegmon can’t be easily drained.

Phlegmon is frequently caused by bacteria, most often group A streptococcus or Staphylococcus aureus.

  • Bacteria may enter via a scratch, insect bite, or injury to form a phlegmon just under the skin on your finger or feet.
  • Bacteria in your mouth can cause an oral phlegmon or abscess, especially after dental surgery.
  • Bacteria can also attach to the wall of an internal organ such as the stomach wall or the appendix and form phlegmon

People with compromised immune systems may be especially vulnerable to phlegmon formation.

Symptoms of phlegmon vary, depending on the location and severity of the infection. If not treated, an infection can spread to deeper tissue and disable the limb or area involved.

Skin phlegmon

Skin phlegmon can be:

  • red
  • sore
  • swollen
  • painful

You may also have systemic signs of a bacterial infection, such as:

  • swollen lymph glands
  • fatigue
  • fever
  • headache

Phlegmon and internal organs

Phlegmon can affect any internal organ. Symptoms vary by the organ involved and the particular bacteria.

General symptoms are:

  • pain
  • disruption of organ function

Some location-specific symptoms may include:

Intestinal tract

  • abdominal pain
  • fever
  • nausea
  • vomiting


  • pain
  • fever
  • vomiting
  • diarrhea
  • intestinal blockage


  • pain
  • floaters
  • disrupted vision
  • flu-like symptoms

Mouth floor (a phlegmon here is also called Ludwig’s angina)

  • dental pain
  • fatigue
  • ear pain
  • confusion
  • swelling of tongue and neck
  • difficulty breathing


  • fever
  • increase in white blood cells (leukocytosis)
  • increased blood levels of amylase (a pancreatic enzyme)
  • severe stomach pain
  • nausea and vomiting


  • fever
  • sore throat
  • difficulty speaking
  • hoarseness

Your doctor will ask about your symptoms, when they started, and how long you’ve had them. They’ll take a medical history and ask about any disease you may have or medications you’re taking. They’ll also give you a physical examination.

Skin phlegmon are visible. Internal phlegmons are more challenging to diagnose. Your doctor will feel for lumps or tenderness in the area of pain. They’ll also order tests, which may include:

  • blood workup
  • urine analysis
  • ultrasound
  • X-ray
  • MRI
  • CT scan

To distinguish among cellulitis, abscess, and phlegmon, your doctor may use intravenous gadolinium with MRI to show the outline of an abscess “wall” vs. phlegmon.

Contrast-enhanced ultrasound may be used to identify phlegmon in the abdominal area.

Treatment for phlegmon depends on the location and seriousness of the infection. In general, treatment involves both antibiotics and surgery.

Skin phlegmon, if minor, may be treated with oral antibiotics. But surgery may be needed to clean dead tissue from the area and stop the infection from spreading.

Oral phlegmon can spread quickly and can be life-threatening. Aggressive early use of antibiotics is recommended along with intubation (placement of a breathing tube in the trachea). Surgery as soon as possible to drain the area and stop the spread of the infection is also recommended.

Before antibiotics were developed, 50 percent of people with phlegmon in the mouth area died.

The outlook for phlegmon depends on the severity of the infection and the area that’s infected. Prompt medical attention is always necessary.

Antibiotics are usually required to kill the infection. Surgery is often needed, but in some cases conservative management may be enough to resolve the phlegmon. Discuss with your doctor whether a nonsurgical treatment may work for you or your child.

With treatment, the general outlook for phlegmon is good.