Cellulitis is an infection of the deeper layers of the skin and the underlying tissue.
The main symptom of cellulitis is the affected area of skin suddenly turning red, painful swollen and hot.
Cellulitis can have a wide range of causes, but the majority of cases are caused by a type of bacteria called group A streptococcus, or a different type of bacteria called staphylococcus aureus.
The skin is the largest organ of the human body. It is made up of three main layers:
- the epidermis – the outer surface of skin and an underlying section of cells, which the body uses to create new skin cells
- dermis – the middle layer of skin that contains blood vessels, sweat glands and hair follicles
- subcutis – the bottom layer of skin that consists of a layer of fat and collagen (a tough, spongy protein), which helps protect the body and regulate temperature
Causes of cellulitis
Cellulitis develops when bacteria, or sometimes fungi, move down through the skin’s surface into the dermis and subcutis through a damaged or broken area of skin, such as a cut, burn or bite.
Having a skin condition such as eczema or a fungal infection of the foot or toenails (athlete’s foot) can cause small breaks and cracks to develop in the surface of the skin. This makes a person more vulnerable to cellulitis.
Other known risk factors for cellulitis include:
- having a weakened immune system (the body’s natural defence against infection and illness) as a result of health conditions such as HIV or diabetes, or as a side effect of a treatment such as chemotherapy
- lymphoedema – a condition that causes swelling of the arms and legs, which can sometimes occur spontaneously or may develop after surgery for some types of cancer
- intravenous drug misuse (injecting drugs such as heroin)
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Symptoms of cellulitis
Cellulitis causes affected skin to become red, swollen, hot and tender.
It most often affects the legs, but can occur anywhere on the body.
See your GP immediately if an area of skin suddenly turns red, hot and tender. If you cannot see your GP on the same day, you should go to a walk-in centre or minor injuries unit.
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Certain symptoms can indicate that the infection has spread from your skin to other parts of the body, such as the blood. These include vomiting, fever, rapid breathing and confusion or disorientation. If you experience these symptoms, call 999 for an ambulance.
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Who is affected?
Cellulitis can affect people of all ages, including children. Rates are thought to be roughly similar in both sexes.
In England in 2009, around 80,000 people were admitted to hospital as a result of cellulitis. The number of annual cases of cellulitis has increased three-fold over the past 15 years.
Cellulitis usually responds well to treatment with antibiotics if it's diagnosed and treated promptly.
As a precaution, hospital admission is usually recommended for more severe cases of cellulitis that fail to respond to antibiotic tablets.
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In some cases of cellulitis the bacteria triggers a secondary infection somewhere else in the body, such as in the blood (septicaemia). Such cases usually require hospital admission for treatment with intravenous antibiotics (antibiotics given directly into a vein).
In 2010, there were 917 deaths as a result of cellulitis in England and Wales. Most of these deaths occurred in elderly people.
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