A carbuncle is an abscess larger than a boil, usually with one or more openings draining pus onto the skin. It is usually caused by bacterial infection. Most carbuncles are caused by the bacteria staphylococcus aureus. The infection is contagious and may spread to other areas of the body or other people.

A carbuncle is made up of several skin boils (furuncles). The infected mass is filled with fluid, pus, and dead tissue. Fluid may drain out of the carbuncle, but sometimes the mass is so deep that it cannot drain on its own.

Carbuncles may develop anywhere, but they are most common on the back and the nape of the neck. Men get carbuncles more often than women.

Because the condition is contagious, several family members may develop carbuncles at the same time. Often, the direct cause of a carbuncle cannot be determined.

Things that make carbuncle infections more likely include:

Friction from clothing or shaving

Poor hygiene

Poor overall health

Persons with diabetes, dermatitis, and weakened immune systems are more likely to develop staph infections.