Cellulitis (Deep Infection Under the Skin)

What is cellulitis?

Cellulitis is an infection of the tissue just underneath the skin (subcutaneous tissue) most commonly occurring on the legs, arms or face. It is a serious infection that requires prolonged antibiotic treatment or the bacteria can spread thereby leading to sepsis (“blood poisoning”). Cellulitis can occur in any person but is more often seen in diabetics and people with compromised immune systems like HIV and AIDS patients. With multi-drug resistant bacteria being widespread, cellulitis is often difficult to treat especially when a person does not have the immune defences to combat the infection.

Cellulitis Symptoms

First the infected area becomes red, swollen and tender. With time pain sets in and the lymph nodes in and around the area may become swollen and tender. The area tends to feel hot to touch compared to the surrounding unaffected skin. Tiny red blisters may form on the skin surface around the cut or open wound.

There may be a soft spongy feeling to the affected tissue and sometimes there may be abscess formation (boil) under the skin which feels firm and round. If the abscess bursts then pus may ooze out of the site of the cut or wound. Long red streaks may be visible on the skin surface which is in line with the inflamed lymphatic vessels.A fever is usually present although it may not arise at the outset.

Causes and Risks

Cellulitis arises when bacteria gain entry into the deeper tissue through a break in the skin. It can be from a simple deep cut or a large wound. Normally the skin acts as a barrier protecting the inner tissue of the body from the environment. The immune system offers a second line of defence by attacking and destroying any microbes that enter through the skin. However, with cellulitis the immune system may not be able to deal with a large influx of bacteria, or the immune system is too weak to fight off the bacteria. The infection may then spread to neighbouring tissue, involve the lymphatics in the area and in severe cases even spread through the bloodstream throughout the body.

Bacteria that cause cellulitis

Various different types of bacteria can cause cellulitis. Often it is the naturally occurring bacteria that cause the infection once it gains entry into the deeper tissue under the skin. Streptococci and staphylococci are two of the most common groups of bacteria that cause cellulitis. Although these bacteria can easily be eradicated with antibiotics, these days multi-drug resistant strains have emerged which have posed a problem for conventional antibiotic treatment. MRSA (multi-drug resistant Staphylococcus aureus) is one such type of resistant bacteria that causes cellulitis which is difficult to treat. Once the bacteria gain entry into the underlying tissue, it has a warm, moist and nutrient rich environment to grow and thrive.

Why are the legs most commonly affected?

Cellulitis can occur at any site on the body. However, the legs are more commonly affected for several possible reasons. Firstly, the legs are prone to injury, whether from a fall, a cut or insect bites, compared to other sites. Secondly, the circulation is the most sluggish in the leg meaning that immune cells responding to invading microbes cannot reach the site as speedily or effectively. The local immune defences are also not as efficient. However, this is not usually a problem in most healthy people. When there is a problem with circulation in the legs, poor wound healing due to various diseases, high blood sugar levels like in diabetes and an overall weakened immune system (like with HIV/AIDS) then cellulitis is more likely to occur.

Who is at risk of cellulitis?

Any person can develop cellulitis if bacteria gain entry into the underlying tissue beneath the skin and if the immune system cannot eradicate the bacteria in time. People who are more likely to develop cellulitis includes :

  • Those with skin disorders like eczema where the skin is not able to fulfil its protective barrier function. Furthermore repeated scratching due to itching in these skin disease may increase the chances of bacteria being introduced into the deeper tissue.
  • Chronic circulation problems in the leg that leads to swelling and open sores (ulcers).
  • Poor wound healing as is seen in conditions like diabetes mellitus (sugar diabetes).
  • Not properly treating a deep wound and keeping it “clean” by using disinfectants and appropriate dressings on the wound.
  • Weakness immune systems as is seen with HIV/AIDS and various other diseases.
  • Intravenous drug use where “dirty” needles introduce the bacteria into the tissue under the skin.

Treatment of Cellulitis

Cellulitis needs to be treated with antibiotics. In most cases oral antibiotics are sufficient but in severe cases a person may need to be hospitalized and intravenous (IV) antibiotics administered. Although the symptoms of cellulitis may ease to a large degree within a few days after starting antibiotics, the entire course of the pills needs to be completed. If not, the infection can recur and may be more difficult to treat.

Cellulitis may require antibiotic treatment for as long as 10 to 14 days and at times a second course of antibiotics may be prescribed. Proper wound care with the use of an antimicrobial cream will also ensure that the primary site heals and new bacteria do not enter the wound. Cellulitis is a very serious infection that can lead to death if it is left untreated.EE