An abscess is an enclosed collection of liquefied tissue, known as pus, somewhere in the body. It is the result of the body’s defensive reaction to foreign material.
There are two types of abscesses, septic and sterile. Most abscesses are septic, which means that they are the result of an infection. Septic abscesses can occur anywhere in the body. Only a germ and the body’s immune response are required. In response to the invading germ, white blood cells gather at the infected site and begin producing chemicals called enzymes that attack the germ by digesting it.
These enzymes act like acid, killing the germs and breaking them down into small pieces that can be picked up by the circulation and eliminated from the body. Unfortunately, these chemicals also digest body tissues. In most cases, the germ produces similar chemicals. The result is a thick, yellow liquid—pus—containing digested germs, digested tissue, white blood cells, and enzymes.
An abscess is the last stage of a tissue infection that begins with a process called inflammation. Initially, as the invading germ activates the body’s immune system, several events occur:
* Blood flow to the area increases.
* The temperature of the area increases due to the increased blood supply.
* The area swells due to the accumulation of water, blood, and other liquids.
* It turns red.
* It hurts, because of the irritation from the swelling and the chemical activity.
These four signs—heat, swelling, redness, and pain—characterize inflammation.
As the process progresses, the tissue begins to turn to liquid, and an abscess forms. It is the nature of an abscess to spread as the chemical digestion liquefies more and more tissue. Furthermore, the spreading follows the path of least resistance—the tissues most easily digested. A good example is an abscess just beneath the skin. It most easily continues along beneath the skin rather than working its way through the skin where it could drain its toxic contents. The contents of the abscess also leak into the general circulation and produce symptoms just like any other infection. These include chills, fever, aching, and general discomfort.
Sterile abscesses are sometimes a milder form of the same process caused not by germs but by non-living irritants such as drugs. If an injected drug like penicillin is not absorbed, it stays where it was injected and may cause enough irritation to generate a sterile abscess— sterile because there is no infection involved. Sterile abscesses are quite likely to turn into hard, solid lumps as they scar, rather than remaining pockets of pus.
Causes and symptoms
Many different agents cause abscesses. The most common are the pus-forming (pyogenic) bacteria like Staphylococcus aureus, which is nearly always the cause of abscesses under the skin. Abscesses near the large bowel, particularly around the anus, may be caused by any of the numerous bacteria found within the large bowel. Brain abscesses and liver abscesses can be caused by any organism that can travel there through the circulation. Bacteria, amoeba, and certain fungi can travel in this fashion. Abscesses in other parts of the body are caused by organisms that normally inhabit nearby structures or that infect them. Some common causes of specific abscesses are:
* skin abscesses by normal skin flora
* dental and throat abscesses by mouth flora
* lung abscesses by normal airway flora, pneumonia germs, or tuberculosis
* abdominal and anal abscesses by normal bowel flora
Specific types of abscesses
Listed below are some of the more common and important abscesses.
* Carbuncles and other boils. Skin oil glands (sebaceous glands) on the back or the back of the neck are the ones usually infected. The most common germ involved is Staphylococcus aureus. Acne is a similar condition of sebaceous glands on the face and back.
* Pilonidal abscess. Many people have as a birth defect a tiny opening in the skin just above the anus. Fecal bacteria can enter this opening, causing an infection and subsequent abscess.
* Retropharyngeal, parapharyngeal, peritonsillar abscess. As a result of throat infections like strep throat and tonsillitis, bacteria can invade the deeper tissues of the throat and cause an abscess. These abscesses can compromise swallowing and even breathing.
* Lung abscess. During or after pneumonia, whether it’s due to bacteria [common pneumonia], tuberculosis, fungi, parasites, or other germs, abscesses can develop as a complication.
* Liver abscess. Bacteria or amoeba from the intestines can spread through the blood to the liver and cause abscesses.
* Psoas abscess. Deep in the back of the abdomen on either side of the lumbar spine lie the psoas muscles. They flex the hips. An abscess can develop in one of these muscles, usually when it spreads from the appendix, the large bowel, or the fallopian tubes.