Boils and carbuncles are skin infections usually caused by Staphylococcus aureus bacteria (staph). These staph infections form pockets in the skin that are filled with pus, a fluid that includes bacteria, dead skin cells and infection-fighting white blood cells. Whether the pocket of pus is called a boil or a carbuncle depends on its location and size:
A boil, also called a furuncle, begins as a painful infection of a single hair follicle. Boils can grow to be larger than a golf ball, and they commonly occur on the buttocks, face, neck, armpits and groin.
A carbuncle is a deeper skin infection that involves a group of infected hair follicles in one skin location. Carbuncles often are found on the back of the neck, shoulders, hips and thighs, and they are especially common in middle-aged or elderly men. People with diabetes are more likely to develop carbuncles.