A pilonidal cyst is a fluid-filled defect. It is found at the base of the spine, or “tailbone” area.
The terms cyst, sinus, and abscess refer to different stages of the disease process.
When a pilonidal cyst is infected, it forms an abscess, eventually draining pus through a sinus. Pilonidal cysts are harmless until they get infected. At this point they form an abscess that causes pain, a foul smell, and drainage. This is more likely to occur in young Caucasian men with a lot of hair in the region.