An abscess () is pus that has built up within the tissue of the body. Signs and symptoms of abscesses include: redness, pain, warmth, and swelling. This swelling feels like it is filled with fluid if it is pressed. The area of redness is often bigger than the area of swelling. Carbuncles are an abscess in the hair follicles.

An abscess is usually caused by a bacterial infection. Often many different types of bacteria can be part of a single infection. In the United States and many other areas of the world the most common bacteria present is MRSA (methicillin-resistant Staphylococcus aureus). Rarely parasites can cause abscesses and this is more common in the developing world. Diagnosis of a skin abscess is usually made based on what it looks like and is proved by cutting it open. Ultrasound imaging may be useful in cases in which the diagnosis is not clear. In abscesses around the anus, computer tomography (CT) may be important to look for deeper infection.

Treatment for most skin or soft tissue abscesses is to cut it open and drain out the pus. Antibiotics are usually not needed for healthy people. New studies have found that it is better to close the wound after draining, instead of packing it with gauze. This can speed healing and not increase risk of the abscess returning.  Sometimes simply sucking out the pus with a needle is not enough.

Skin abscesses are common and have become more common in recent years. As many as 65% of people who take intravenous drugs get abscesses In 2005 in the United States 3.2 million people went to the emergency department for an abscess. In Australia around 13,000 people were put in hospital in 2008 for the disease.

Signs and symptoms

Abscesses can form in any kind of solid tissue. They are usually on the skin surface (such as a boils, or deep skin abscesses), in the lungs, brain, teeth, kidneys and tonsils.  The condition can become more complicated if the pus and the infection spread to other parts of the body. This can lead to gangrene, where areas of body tissue die.

The main symptoms and signs of a skin abscess are redness, heat, swelling, pain and loss of function. There may also be high temperature (fever) and chills.

Internal abscesses are more difficult to find. The abscess can be painful, and a person will have a high temperature, and generally feel unwell.
Internal abscesses do not usually heal without medical treatment. In some cases an abscess could even cause death, for example where an abscess in the neck put pressure on the trachea.

If abscess is on the surface, it may be "fluctuant", that is it feels like it is full of fluid, when touched. This is a wave-like motion caused by movement of the pus inside the abscess.

Causes
Abscesses are caused by bacterial infection, parasites, or foreign substances.
Bacterial infection is the most common cause. Often many different types of bacteria are involved in a single infection. In the United States and many other areas of the world the most common bacteria present is MRSA. Among spinal subdural abscesses, methicillin-sensitive Staphylococcus aureus is the most common organism involved.

Rarely parasites can causes abscesses and this is more common in the developing world. Specific parasites known to do this include: dracunculiasis and myiasis.

References

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