What Is Cellulitis?

A common infection of the skin

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Cellulitis is a common infection of the skin, almost always caused by bacteria. The infection can come on suddenly and usually spreads from the skin surface and then goes deeper. It spreads below the epidermis, the top layer of skin, into the dermis and the subcutaneous fat. It can cause redness, skin swelling, pain, heat at the site, and possibly fever.

Cellulitis often infects the leg and sometimes the face, hands, or arms. It usually affects only one place at a time—for example, just one leg, not both.

Causes

Cellulitis can begin with a nick in the skin, whether through a cut, a bite, or a burn.

Other skin conditions, like eczema or athlete’s foot, can cause small breakdowns in the skin and can lead to cellulitis. Those who have swelling in their legs such as from venous stasis or lymphedema (e.g., after surgery for breast cancer), those with varicose veins, or those who have had vein grafts taken tend to have more cases of cellulitis, as they cannot clear bacteria as quickly, allowing the bacteria to survive, divide, and cause infections.

Other risk factors for cellulitis also include obesity, leg swelling, and diabetes. Foot checks performed by a healthcare provider are important in those with diabetic neuropathy to make sure they don’t have any skin breakdown, ulcers, or wounds if they can’t see for themselves.

Cellulitis is more common in older adults but can happen in any age group and either gender. One study published in 2006 found that about one in 400 people will develop cellulitis each year. 

Types of Cellulitis

Cellulitis infections are often caused by the bacteria Staphylococcus aureus (including methicillin-resistant Staphylococcus aureus [MRSA]) and Group A Streptococcus. Many cases of Staph aureus are now resistant to the antibiotics that once worked.

Rare Types

There are a few rare causes of less common types of cellulitis. Some of these can be dangerous in those at risk—such as those who are immunosuppressed, have diabetes, lack a spleen, or have liver problems.

Cat bites, which can be deep and more dangerous than commonly realized, can introduce Pasteurella multocida, leading to serious infections of the skin and deeper structures. Dog bites can in rare cases lead to a serious cause of infection, Capnocytophaga, which is very dangerous in those who do not have spleens.

Exposure to warm salt water, such as from a walk on the beach, especially in those with liver or alcohol problems, can lead to Vibrio vulnificus. This is a serious infection which can be fatal if not quickly treated.

Freshwater exposure can be associated with Aeromonas hydrophila infections. Children sometimes have infections with Haemophilus influenza.

Surgery can lead to cellulitis, even rare types like mycobacterial infections. Those who are immunocompromised can be prone to a wide range of infections, like Pseudomonas, Proteus, Fusarium, and Serratia.

Those at risk may require different antibiotics up front, even though most cellulitis cases are caused by either Staph or Strep infections.

Cellulitis can also be confused with a DVT (deep vein thrombosis), which requires very different treatment. It is important to talk to your healthcare provider to make the right diagnosis.

Treatment

Treatment usually consists of oral antibiotics. Most patients get better quickly and do not require hospitalization.

Because it is uncommon for people with cellulitis to discover the exact type of bacteria causing the infection (there is rarely any testing performed to show which type of bacteria is responsible), healthcare providers often have to make educated guesses about what the likeliest bacteria are and base treatment on those guesses. This is called empiric therapy.

Using empiric therapy, antibiotics are selected by the healthcare provider to cover the most likely types of bacteria, depending on what specific risks the patient has. Because MRSA can cause cellulitis but is often resistant to common antibiotics, empiric antibiotics treating MRSA should sometimes be given to patients with cellulitis to increase the chance that antibiotics will work.

It may be helpful to draw a line around the borders of an infection if it is visible in order to determine whether the cellulitis is growing or receding. It can be hard to tell overnight if the cellulitis has gotten better or worse.

If there is swelling or the person does not have good vein or lymph flow, lift the leg or arm affected to let the fluid drain.

It is common that the infection does not quickly recede. It may take a day or two to really see the infection fading.

However, if someone becomes more ill or febrile, or the infection is not diminishing, they may need to be hospitalized and may need IV antibiotics.

Pictures of Cellulitis

This photo contains content that some people may find graphic or disturbing.

Cellulitis on a foot
Cellulitis on a foot.

Wendy Townrow / Getty Images

This photo contains content that some people may find graphic or disturbing.

Cellulitis on an ankle
Cellulitis on an ankle.

LagunaticPhoto / Getty Images

This photo contains content that some people may find graphic or disturbing.

cellulitis on a leg
Cellulitis on a leg.

DR P. MARAZZI / SCIENCE PHOTO LIBRARY / Getty Images

This photo contains content that some people may find graphic or disturbing.

Cellulitis on a leg
Cellulitis on a leg.

Wendy Townrow / Getty Images

Complications

Several complications may arise as a result of cellulitis.

Necrotizing Fasciitis

Necrotizing fasciitis is a rare infection of the deeper layers of skin, reaching down to the fascia below. It causes extreme pain and can spread very quickly. It can quickly lead to the death of the tissues in these layers (subcutaneous and fascia), and in turn lead to the death of the patient, especially if treatment (surgery and antibiotics) is not rapidly available.

Sepsis

Sepsis can occur when the bacteria from the skin reach deeper and spread through the blood, seeding other parts of the body. This can be very serious, requiring hospitalization and IV antibiotics.

Abscesses

Abscesses can form from severe infections. An abscess is a pocket of infection that can be difficult to clear. It may need drainage and not just antibiotics.

Orbital Cellulitis

Orbital cellulitis can occur when bacteria spread to the areas around the eye (behind the orbital septum). Any pain with moving the eye, inability to open the eye, infection around the eye, or swelling of the eyelid should be taken seriously. It is more common in children.

This type of cellulitis usually involves the spread of bacteria from a cellulitis in front and around the eye or from the sinuses (or bloodstream) to the eye socket. It is not the same as periorbital cellulitis, which refers to an infection only in front of the eye and not deeper into the eye socket.

Orbital cellulitis is a serious infection which can lead to loss of sight and even spread of bacteria to the meninges or brain.

A Word From Verywell

Cellulitis is a skin infection that comes on quickly and can turn serious. While some bacteria live on the skin at all times and are generally harmless, if they enter the skin, they can cause infection.

If you notice any swelling, redness, pain, or heat at a site where you’ve had a cut, bite, or burn on your body, seek medical care immediately.

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10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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