It is similar to a boil but instead of affecting just one hair follicle, a carbuncle involves several contiguous follicles. A carbuncle tends to spread locally, sometimes forming clusters with several openings that discharge pus.
Carbuncles occur most commonly on the back of the neck, buttocks, and thighs.
The infection is usually treated with antibiotics taken under medical supervision, but sometimes a physician has to make an incision to drain a carbuncle. See also BOIL .