A carbuncle is a large cluster of boils, or furuncles, situated under the skin in a connected area of the body. Carbuncles and boils are caused by a bacterial infection under the skin, usually infecting a hair follicle in an area exposed to sweat and friction.
A carbuncle is initially caused by a bacterial infection, such as Staphylococcus aureus, in areas of high hair growth including the face, neck, armpits and buttocks. Furuncles and carbuncles are commonly found in areas covered by clothing that can cause high temperatures and friction against the body. A furuncle usually begins under the skin and becomes visible as a tender, red, inflamed area on the skin approximately the size of a pea.
Because a carbuncle is caused by multiple hair follicles becoming infected and inflamed beneath the skin, the size of the tender, red area is larger than that of a single boil or furuncle. The inflamed area of the furuncle begins to swell and becomes more painful as the carbuncle fills with pus as the infection beneath the skin spreads to connected areas of the body. The onset of a carbuncle can be accompanied by physical symptoms including a general unwell feeling, chills and a fever.
A carbuncle can grow until it becomes a large, red, inflamed area with a yellowish-white tip that continues growing until it ruptures and eventually drains. Because the infection within a carbuncle is stronger than that within a boil or furuncle, a carbuncle can drain pus and bloody discharge over a long period of time without healing sufficiently. The pus-filled area where a carbuncle forms should not be squeezed or popped without medical assistance because the pus can spread the infection across the skin into other areas.
Boils and carbuncles can occur in children or adults of any age. Children are especially susceptible due to lower hygiene standards and weaker immune systems. Children and older adults who have a boil or carbuncle should seek medical treatment, according to the Mayo Clinic. Others who should seek treatment include those with a low immune system, such as people infected with HIV or who have had an organ transplant. Deep scarring or pitted areas are more likely to result from a carbuncle than from a boil.