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Definition

Cellulitis is a common skin infection caused by bacteria. It affects the middle layer of the skin (dermis) and the tissues below. Sometimes, muscle below the skin can be affected.

Skin layers
The skin is the largest organ of the body. The skin and its derivatives (hair, nails, sweat and oil glands) make up the integumentary system. One of the main functions of the skin is protection. It protects the body from external factors such as bacteria, chemicals, and temperature. The skin contains secretions that can kill bacteria and the pigment melanin provides a chemical pigment defense against ultraviolet light that can damage skin cells. Another important function of the skin is body temperature regulation. When the skin is exposed to a cold temperature, the blood vessels in the dermis constrict. This allows the blood which is warm, to bypass the skin. The skin then becomes the temperature of the cold it is exposed to. Body heat is conserved since the blood vessels are not diverting heat to the skin anymore. Among its many functions the skin is an incredible organ always protecting the body from external agents.

Alternative Names

Skin infection - bacterial; Group A streptococcus - cellulitis; Staphylococcus - cellulitis

Causes

Staphylococcus and streptococcus bacteria are the most common causes of cellulitis.

Normal skin has many types of bacteria living on it. When there is a break in the skin, these bacteria can cause a skin infection.

Risk factors for cellulitis include:

  • Cracks or peeling skin between the toes
  • History of peripheral vascular disease
  • Injury or trauma with a break in the skin (skin wounds)
  • Insect bites and stings, animal bites, or human bites
  • Ulcers from certain diseases, including diabetes and vascular disease
  • Use of corticosteroid medicines or other medicines that suppress the immune system
  • Wound from a recent surgery

Symptoms

Symptoms of cellulitis include:

Exams and Tests

Your health care provider will perform a physical exam. This may reveal:

  • Redness, warmth, tenderness, and swelling of the skin
  • Possible drainage, if there is a buildup of pus (abscess) with the skin infection
  • Swollen glands (lymph nodes) near the affected area

Your provider may mark the edges of the redness with a pen, to see if the redness goes past the marked border over the next several days.

Tests that may be ordered include:

Treatment

You will likely be prescribed antibiotics to be taken by mouth. You may be given pain medicine as well, if needed.

At home, raise the infected area higher than your heart to reduce swelling and speed up healing. Rest until your symptoms improve.

You may need to stay in a hospital if:

  • You are very sick (for example, you have a very high temperature, low blood pressure, or nausea and vomiting that does not go away)
  • You have been on antibiotics and the infection is getting worse (spreading beyond the original pen marking)
  • Your immune system is not working well (due to cancer, HIV, or other medical condition)
  • You have an infection around your eyes
  • You require antibiotics through a vein (IV)

Outlook (Prognosis)

Cellulitis usually goes away after taking antibiotics for 7 to 10 days. Longer treatment may be needed if cellulitis is more severe. This may occur if you have a chronic disease or your immune system is not working properly.

People with fungal infections of the feet may have cellulitis that keeps coming back, especially if you have diabetes. Cracks in the skin from the fungal infection allow the bacteria to get into the skin.

Possible Complications

The following may result if cellulitis isn't treated or treatment doesn't work:

When to Contact a Medical Professional

Call your provider right away if:

  • You have symptoms of cellulitis
  • You are being treated for cellulitis and you develop new symptoms, such as persistent fever, drowsiness, lethargy, blistering over the cellulitis, or red streaks that spread

Prevention

Protect your skin by:

  • Keeping your skin moist with lotions or ointments to prevent cracking
  • Wearing shoes that fit well and provide enough room for your feet
  • Learning how to trim your nails to avoid harming the skin around them
  • Wearing appropriate protective equipment when participating in work or sports

Whenever you have a break in the skin:

  • Clean the break carefully with soap and water. Apply petroleum jelly every day.
  • Cover with a bandage and change it every day.
  • Watch for redness, pain, drainage, or other signs of infection.

Gallery

Skin layers
The skin is the largest organ of the body. The skin and its derivatives (hair, nails, sweat and oil glands) make up the integumentary system. One of the main functions of the skin is protection. It protects the body from external factors such as bacteria, chemicals, and temperature. The skin contains secretions that can kill bacteria and the pigment melanin provides a chemical pigment defense against ultraviolet light that can damage skin cells. Another important function of the skin is body temperature regulation. When the skin is exposed to a cold temperature, the blood vessels in the dermis constrict. This allows the blood which is warm, to bypass the skin. The skin then becomes the temperature of the cold it is exposed to. Body heat is conserved since the blood vessels are not diverting heat to the skin anymore. Among its many functions the skin is an incredible organ always protecting the body from external agents.
Poison oak rash on the arm
Poison oak rash on the arm. Several plants produce toxins that cause skin reaction. This is the appearance of poison oak dermatitis. Note the typical linear streaks produced either by scratching or brushing against the plant. (Image courtesy of the Centers for Disease Control and Prevention.)
Cellulitis
Cellulitis is a deep infection of the skin, usually accompanied by generalized (systemic) symptoms such as fever and chills. The area of redness increases in size as the infection spreads. The center of the circled lesion has been biopsied.
Graves disease
Graves disease is an autoimmune disorder that involves overactivity of the thyroid (hyperthyroidism). Hallmarks of the condition are bulging eyes (exophthalmos), heat intolerance, increased energy, difficulty sleeping, diarrhea and anxiety.

References

Dinulos JGH. Bacterial infections. In: Dinulos JGH, ed. Habif's Clinical Dermatology. 7th ed. Philadelphia, PA: Elsevier; 2021:chap 9.

Gabel C, Ko L, Kroshinsky D. Cellulitis and erysipelas. In: Lebwohl MG, Heymann WR, Coulson IH, Murrell DF, eds. Treatment of Skin Disease: Comprehensive Therapeutic Strategies. 6th ed. Philadelphia, PA: Elsevier; 2022:chap 39.

Pasternack MS, Swartz MN. Cellulitis, necrotizing fasciitis, and subcutaneous tissue infections. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 93.

Last reviewed May 31, 2023 by Ramin Fathi, MD, FAAD, Director, Phoenix Surgical Dermatology Group, Phoenix, AZ. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team..

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