What Is It?
An infection inside the tip of the finger can form an enclosed pocket of pus (or abscess) that is very painful as it expands. A felon is a fingertip abscess deep in the palm side of the finger. It usually is caused by bacterial infection, most often from growth of Staphylococcus aureus bacteria.
A painful bump on the end of a finger that is sometimes mistaken for a felon is a herpes virus infection that forms a herpetic whitlow.