Cellulitis - An Infection of the Skin

Cellulitis can come on suddenly

cellulitis. Getty

Cellulitis is very common. It can come on suddenly in almost anyone.

Cellulitis is an infection of the skin, almost always caused by bacteria. The infection usually spreads from the skin surface .and then goes deeper. It spreads below the epidermis, the top layer of skin, and into the dermis and into 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, just one leg, not both.

Cellulitis can begin with a nick in a 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 (such as after surgery for breast cancer) have more cases of cellulitis, as they cannot clear infections as quickly. Those who have had vein grafts taken (when lymphatic fluid backs up, such as for heart surgery) or have varicose veins also have more cellulitis. Other risk factors for cellulitis also include obesity, leg swelling, and diabetes. Those with diabetes should have foot checks to make sure they don't have any skin breakdown or cellulitis if they can't see for themselves.

It is more common in older adults, but can happen in any age group and either gender.

There are different types of cellulitis.

Infections are often caused by the bacteria Staphylococcus Aureus and Group A Streptococcus. Many cases of Staph Aureus are resistant to the antibiotics that once worked. Many infections need to empirically be treated for MRSA.

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

Bites by cats, which are be deeper and more dangerous than thought, can lead to Pasteurella multocida. Dog bites can rarely lead to one 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 and can be fatal if not quickly treated. Fresh water 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, Serratia.

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

It can also be confused with a DVT (Deep Vein Thrombosis) which requires very different treatment. It is important to talk to your doctor to make the right diagnosis.


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

There are antibiotics that are given standardly for cellulitis. There is rarely any testing performed to show which type of bacteria is responsible. Antibiotics are selected by a doctor to cover the most likely types of bacteria, depending on what specific risks the person has.

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

There are a few dangerous complications of cellulitis.

  • 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 death of the tissues in these layers (subcutaneous and fascia). It can lead to death, especially if treatment (surgery and antibiotics) is not rapidly available.
  • 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 can form from severe infections.  An abscess is a pocket of infection and can be more difficult to clear. It may need drainage and not just antibiotics.
  • 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. It 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 a periorbital cellulitis which refers to an infection only in front of the eye and not deeper into the eye socke. Orbital cellulitis is a serious infection which can lead to loss of sight and even spread of bacteria to the meninges or brain.

How common is Cellulitis?

Cellulitis is pretty common. One study found almost 1 in 400 will develop cellulitis a year – more in those who are older.  Other studies of younger adults under 40 known to be healthy (and in the military) found a rate of 2 in 10,000. Rates increase with age and other illnesses.

Continue Reading