A carbuncle is typically the result of neglected skin infection in a dirty, malnourished, and underprivileged patient, particularly a diabetic. A staphylococcal infection starts in one of his hair follicles, usually at the back of his neck or on the back of a finger (8.1), and then spreads. In doing so the infection lifts the skin above it on a sea of necrotic fat and pus. By the time you see him, pus will probably be discharging. Antibiotics don't cure a carbuncle, although they may stop it spreading. You will probably have to let the slough separate slowly, and then remove it.
CARBUNCLES For the general method, see Section 5.2. Be sure to test the patient's urine for sugar.
If the skin around his carbuncle is hairy, shave it with as little trauma as you can. Wash it with hexachlorophane solution, apply dry gauze, and change this frequently. A large slough will form in the middle of the carbuncle. You may be able to lift the slough off painlessly without an anaesthesic.
If the slough is slow to separate, excise it, and apply a dressing of vaseline gauze.
If the bare area is large, apply a split skin graft, as soon as it is clean and granulating.
If a collection of pus forms, cut down on it and drain it.