A carbuncle is an abscess larger than a boil. It is usually caused by bacterial infection, most commonly Staphylococcus aureus. The infection is contagious and may spread to other areas of the body or other people. Because the condition is contagious, family members may develop carbuncles at the same time and the infected may have several carbuncles at the same time.
Conditions that make carbuncle infections more likely include generally poor hygiene and weakening of immunity. People and children who are malnourished, persons with diabetes and immune system diseases are more likely to develop staphylococcal infections.