health

Bacteria that are commonly found on the skin, especially Staphylococcus
aureus (stah-fih-lo-KAH-kus ARE-ree-us) and Group A β-hemolytic*
Streptococcus (he-muh-LIH-tik strep-tuh-KAH-kus) typically cause most
abscesses, furuncles, and carbuncles. People who have staphylococcus
bacteria residing in their nose (called staph colonization) may be prone to
developing recurrent skin abscesses.
Much of the skin’s surface is covered by hair. At the base of each hair
is a hair follicle, a sac-like pit in which the hair shaft develops and grows.
If the skin around a hair follicle has been damaged in some way, such as
with a cut or a nick on the skin from shaving, bacteria on the skin’s surface
can enter and start to cause an infection. This alerts the body’s immune
system, which walls off the area around the infected hair follicle. As the
body’s defenses go to work, the area fills with pus and becomes inflamed.
When an area of skin contains infected, inflamed hair follicles, the condition
is known as folliculitis (fuh-lih-kyoo-LYE-tis).
A boil usually starts within an area of folliculitis. The growing pus inside
the boil creates pressure and swelling around the infected spot, often forming
a drainage point at the surface of the skin called a head. A carbuncle
typically has many small areas where pus has collected and formed heads.
Abscesses that appear inside the body, such as within the abdomen,
may be caused by types of bacteria different from those that cause skin
infections. For example, an abscess that forms with appendicitis may be
caused by a blockage in the appendix (known as a stone). These abscesses
usually contain bacteria normally found inside the intestine and in bowel
movements. A liver abscess can occur when an infection in the abdomen
spreads or when an infectious agent from somewhere else in the body
travels through the bloodstream and is deposited in the liver.