Abscess on the neck of a young child. An abscess is a collection of pus, surrounded and walled off by damaged and inflamed tissues. The usual cause of an abscess is a local bacterial infection, often by the staphylococcal genus of bacteria, which the body's defense system has been unable to contain. Antibiotics are the usual form of treatment, although it may also be necessary to lance the abscess in order to release the pus.