what is the infection in a boil
For other uses, see Boil (disambiguation). 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.