A
boil, also called a
furuncle, is a deep
folliculitis,
infection of the
hair follicle. It is most commonly caused by infection by the
bacterium Staphylococcus aureus, resulting in a painful swollen area on the
skin caused by an accumulation of
pus and dead tissue. Boils which are expanded are basically pus-filled nodules. Individual boils clustered together are called
carbuncles. Most human infections are caused by coagulase-positive
S. aureus strains, notable for the bacteria's ability to produce
coagulase, an
enzyme that can clot blood. Almost any
organ system can be infected by
S. aureus.