A
felon is a fingertip abscess deep in the palm side of the
finger. It usually is caused by bacterial infection, but a herpes virus called herpetic whitlow and, more rarely, fungi also can cause felons. In herpetic whitlow, small bubble-like cysts on the skin, called vesicles, and repeated episodes are there which distinguish it from bacterial or fungal infection. It is less likely to be the cause in your sister’s case. Hence it can either be bacterial or fungal infection.