Boil. This patient has a red and painful boil (at centre) with a greenish scab and flaking white scales of dead skin. An area of spreading cellulitis surrounds the lesion. A boil is a localized collection of pus which usually starts as an infected hair follicle or sweat gland. Common sites are the back of the neck, groin and armpits. Boils may recur in people with known or unrecognised diabetes or other conditions where general resistance to bacterial infection is impaired. The bacterium Staphylococcus Aureus is the usual infecting agent. Treatment is with antibiotic drugs and surgical drainage if necessary.