An abscess is a place of accumulation of the creamy white, yellow, or greenish fluid, known as pus, surrounded by reddened tissue. It is the result of the body’s inflammatory response to a foreign body or a bacterial, viral, parasitic, or fungal infection. An abscess usually dries out and resolves when it is drained of pus.

The most common parts of the body affected by abscesses are the face, armpits, arms and legs, rectum, sebaceous glands (oil glands), and the breast during lactation.

Most abscesses are septic, which means they are the result of an infection. Abscesses occur when white blood cells (WBCs) gather in response to an infection. They produce oxidants (for example, superoxide radical) and enzymes to digest the invading bacteria, viruses, parasites, or fungi.

The infective agents are then broken down by the WBCs into small pieces that can be transported through the bloodstream and eliminated from the body.

Unfortunately, the enzymes may also digest part of the body’s tissues along with the infective agents. The resulting liquid of this digestion is pus, which contains the remains of the infective agents, tissue, white blood cells, and enzymes.

A sterile abscess is one that is not produced by an infection. It is caused by irritants, such as foreign bodies or injected drugs, and medications that have not been totally absorbed. Sterile abscesses quite often heal into hardened scar tissue.

Common types of abscesses:

• Boils and carbuncles. Sebaceous glands and superficial skin are the places usually infected.
• Dental abscess. An abscess that develops along the root of a tooth.
• Pilonidal abscess. People who have a birth defect involving a tiny opening in the skin just above the anus may have fecal bacteria enter this opening, causing an infection and a subsequent abscess.
• Retropharyngeal, parapharyngeal, peritonsillar abscess. As a result of throat infections like strep throat and tonsillitis, bacteria invade the deeper tissues of the throat and cause a parapharyngeal or peritonsillar abscess. A retropharyngeal abscess is a result of something usually blood-borne, and not from a direct spread of tonsillitis. These abscesses can compromise swallowing and even breathing.
• Lung abscess. During or after pneumonia, an abscess can develop as a complication.
• Liver abscess. Bacteria, parasites, or amoeba from the intestines can spread through the blood to the liver and cause abscesses.
• Psoas abscess. An abscess can develop in the psoas muscles, when an infection spreads from the appendix, the large intestine, or the fallopian tubes.
• Butin abscess. Any blood-borne organism feeding off bacteria that stimulate pus production (pyogenic organisms). Can cause abscesses in possiblymany sites.