Merck Manual

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Quick Facts



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What is cellulitis?

Cellulitis is a bacterial infection in your skin.

  • Cellulitis is a common skin infection that can spread quickly and be very serious

  • The infected area hurts and is red, warm, and swollen

  • Cellulitis is most common on your legs but can happen anywhere

  • If the infection reaches your bloodstream, it can be life threatening

What causes cellulitis?

Cellulitis is caused by germs (bacteria) that get into your skin. Bacteria are most likely to enter your skin where you have a cut, insect bite, scrape, burn, puncture wound, or patches of dry skin.

Cellulitis is often caused by Staphylococcus bacteria (staph infection). The type of staphylococcus known as MRSA is resistant to many antibiotics. A MRSA infection can be hard to treat.

People have a higher risk of getting cellulitis if they:

  • Are overweight

  • Have a weakened immune system that makes it hard for them to fight off infection

  • Have other skin diseases, such as eczema or athlete's foot

  • Already have a swollen arm or leg

  • Use IV drugs

  • Have had cellulitis before

What are the symptoms of cellulitis?

  • Skin redness, swelling, warmth, and pain

  • Sometimes blisters with yellow fluid

  • Sometimes fever and swollen lymph nodes (swollen glands)

Cellulitis usually starts as a small, red patch that's slightly sore. The infected area can get larger quickly. In a couple of days, it could spread from a spot the size of a quarter on your calf to cover your entire lower leg.

If the infection gets into the blood stream, you can have high fever, low blood pressure, and shut down of some of your organs (sepsis).

How can doctors tell if I have cellulitis?

Doctors diagnose cellulitis based on how your skin looks. There are no tests to tell for sure. However, doctors may do tests such as an ultrasound to make sure your leg isn't red and swollen because of a blood clot.

See a doctor immediately if an area on your skin is red, swollen, and painful.

How do doctors treat cellulitis?

  • Antibiotics to kill the bacteria

  • Usually you take the antibiotics by mouth but sometimes, when there is serious infection, by vein (IV) in the hospital

  • If you have cellulitis in your leg, doctors will ask you to elevate it

How can I prevent cellulitis?

  • Keep skin wounds clean, cover them with a bandage, and apply an antibiotic cream for protection

  • Treat fungal foot infections (such as athlete’s foot) and other skin conditions to help heal any breaks in the skin

  • If you have diabetes or poor circulation, examine your feet every day, use a moisturizer, and avoid injury by wearing proper shoes

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