What is Cellulitis?

Cellulitis is an infection of the dermal and subcutaneous skin layers that gives rise to red, swollen, hot and painful skin.

Sometimes the condition develops on areas of broken skin due to an ulcer or surgical wound, for example, although cellulitis can also occur anywhere on the body or face where skin remains intact. The most commonly affected area is the lower leg, particularly where the tibia is located and in the foot. The next most frequently affected area is the arm, followed by the head and neck. Certain forms of cellulitis are sometimes named according to the body region affected such as buccal cellulitis, which affects the cheeks or periorbital cellulitis, which affects the eye socket area.

Cellulitis can be dangerous if it is not treated promptly as it may spread and even lead to septicemia, a severe infection of the blood. Recurrent cellulitis infection can also eventually impair lymphatic drainage and cause chronic swelling in the affected area.

This condition is relatively common and affects individuals of all ages and races, although it is more common among middle-aged and elderly people.

Symptoms

The symptoms of cellulitis are inflammatory signs such as swelling, pain, tenderness, redness and warmth. These symptoms may be accompanied by a fever, sometimes with sweats, chills and swollen lymph nodes. Eventually, the red areas expand in size and small red spots or small blisters may start to appear.

Pathology and causes of cellulitis

The skin is the largest organ in the body and is comprised of three layers which include:

• The epidermis or outer layer of skin.
• The dermis or middle layer of skin where sweat glands, hair follicles and blood vessels are contained.
• The subcutis or bottom skin layer containing fat and collagen, which provides protection and regulates body temperature.

Cellulitis develops when bacteria and sometimes fungi enter the skin surface through an abrasion such as a cut or bruise. More specifically, the most common bacteria to cause this condition are the beta-hemolytic streptococci. Staphylococcus aureas, including the strains resistant to methicillin (MRSA) is another type of bacteria that commonly causes cellulitis. When MRSA has caused the infection, cellulitis can be difficult to treat due to the bacteria’s resistance to antibiotics.

Cellulitis can also be caused by many other types of bacteria such as Pasteurella multocida, which can be caught from a dog or cat scratch or bite. In children aged under 6 yeas, infection with Hemophilus influenza (H. flu) can also cause the condition. When H. flu is the cause, the arms, face and upper torso are usually the regions affected. Another example of a bacteria that can lead to cellulitis is Pseudomonas aeruginosa, a tough bacterial strain that survives in a range of environments and is often found in soil and stagnant water.

Risk factors

Several factors can increase the risk of cellulitis developing and these include:

• Injury – A cut, burn, fracture or even scrape of the skin can increase the risk of infection because broken skin provides an entry point for bacteria.
• Weakened immune system – Conditions that lead to a weakened immune system increase the risk of infection and examples include chronic leukemia, HIV or AIDS, diabetes, kidney disease and circulatory disorders. Certain medications such as corticosteroids can also weaken the immune system.
• Obesity – Obese individuals are more likely to develop cellulitis as these people are more likely to have reduced circulation of the blood and lymphatic fluid.
• Skin conditions – Some skin disorders that lead to breaks in the skin surface such as eczema, chicken pox or athlete’s foot can increase the risk of cellulitis developing.
• Previous cellulitis infection – People with a history of cellulitis infection are more likely to suffer a future or recurrent infection, particularly if the area affected was the lower leg.
• Chronic swelling in the leg or arm – Swollen tissue is more likely to crack and expose the skin to infection with bacteria.

Treatment of cellulitis

Since cellulitis is usually caused by an infective bacteria, it is treated using antibiotics that are suitable for killing the organism. For fungal infections, antifungal agents are used.

In some cases, the antibiotic needs to be administered intravenously because oral administration does not always provide adequate penetration of the inflamed tissues. In all cases of cellulitis, doctors base their treatment choice on a combination of factors including general health status, the specific strain of bacteria and the degree of infection.

Further Reading

• All Cellulitis Content
• Cellulitis – What Causes Cellulitis?
• Cellulitis – Cellulitis Diagnosis
• Cellulitis – Cellulitis Treatment

Written by

Sally Robertson

Sally has a Bachelor's Degree in Biomedical Sciences (B.Sc.). She is a specialist in reviewing and summarising the latest findings across all areas of medicine covered in major, high-impact, world-leading international medical journals, international press conferences and bulletins from governmental agencies and regulatory bodies. At News-Medical, Sally generates daily news features, life science articles and interview coverage.