Causes

Cellulitis is usually the result of bacteria from the Streptococcus and Staphylococcus groups.

These bacteria are common on the surface of the skin, where they are not harmful.

However, if they enter the skin, usually through a cut or scratch, they can cause an infection.

Cellulitis is not usually contagious but can be spread through contact if a person with an open wound touches skin that has an active infection.

Risk factors

Factors that can increase the risk of cellulitis include:

• Age: Cellulitis is more likely to occur during or after middle age.
• Obesity: Cellulitis is more common among people who have excess weight or obesity.
• Leg issues: Swelling (edema) and ulceration can increase the risk of developing the infection.
• Past cellulitis: Research suggests that anyone who has had cellulitis before has an 8–20% chance of it returning, and the infection can reoccur several times within a year.
• Exposure to environmental factors: These include polluted water and some animals, including fish and reptiles.
• Other skin issues: Chickenpox, eczema, athlete’s foot, abscesses, and other skin conditions can increase the risk of bacteria entering the body.
• Lymphedema: This can lead to swollen skin that can crack and allow bacteria to enter.
• Other conditions: People with liver or kidney disease have a higher risk of developing cellulitis.
• Diabetes: If a person is not able to manage their diabetes effectively, problems with their immune system, circulation, or both can lead to skin ulcers.
• Weakened immune system: People may have this if they are older, if they have HIV or AIDS, or if they are undergoing chemotherapy or radiotherapy.
• Circulatory problems: People with poor blood circulation have a higher risk of infection spreading to deeper layers of the skin.
• Recent surgery or injury: This increases the risk of infection.
• IV drugs: Injecting drugs, especially with needles that they have used before, can lead to abscesses and infections under the skin, increasing the risk of cellulitis.