What Causes Cellulitis?

Cellulitis is an infection of the deeper skin tissues that leads to redness, pain and swelling across affected areas.

The most common cause of cellulitis is bacterial infection. Bacteria that make up the natural flora of the skin such as group A Streptococcus or Staphylococcus aureus often cause cellulitis if they penetrate the skin surface and enter the dermis and subcutaneous skin layer. Fungal infection may also lead to cellulitis.

Some of the common causes and risk factors for cellulitis include:

Broken skin

A cut, graze, abrasion, burn, skin ulcer or insect bite can provide an entry point in the skin’s surface for infective agents to penetrate underlying tissue. Eczema may also give rise to tiny cracks in the surface of the skin that could lead to infection and cellulitis. In many cases of cellulitis, the break in the skin is too small to be identified.


People with diabetes are more prone to cellulitis than the general population as they are more likely to have an impaired immune system. The feet are particularly susceptible because diabetes can reduce circulation in the legs and lead to the development of foot ulcers. In addition, the peripheral neuropathy caused by diabetes can prevent a person form feeling pain as a result of the ulcer, which goes undected while infection progresses.

Weakened immunity

Individuals with a weakened immunity such as the elderly, those taking steroids or chemotherapy agents and people with HIV/AIDS are at an increased risk of cellulitis.

Poor blood circulation

People with poor blood circulation due to conditions such as varicose veins are at an increased risk of cellulitis.


Cellulitis is more common in individuals with lyphoedema which is characterized by swelling due to tissue fluid retention. A dysfunctional lymphatic system may fail to drain fluids from tissues and also prevent infection-fightinh white blood cells from reaching certain areas.

Chicken pox

People with chicken pox or shingles may have a weakened immunity as well as blisters creating openings in the skin and increasing the chance of infection in the deeper skin layers.

Associated microbes

Some of the microbes specifically associated with conditions that can increase the risk for cellulitis include:

  • Diabetes – Staphylococcus aureus, group B streptococci
  • Weakened immunity – Pseudomonas aeruginosa
  • Liver cirrhosis – Vibrio vulnificus, campylobacter fetus
  • Intravenous drug misuse – MRSA (methicillin-resistant Staphylococcus aureus), Pseudomonas aeruginosa

Reviewed by Sally Robertson, BSc

Further Reading

Last Updated: Jun 20, 2023


The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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