Pilonidal sinus is a small hole or channel under the skin and has pus or inflamed fluid accumulation, which may also contain blood. This happens in the cleft, at the lower back, or at the top of the buttocks. Pilonidal cyst or the sinus may also have hair or dirt accumulation, which may cause severe pain and foul-smelling pus or bloody discharge.
People with regular sitting jobs are at a high risk of developing pilonidal sinus or cyst. It is more common in men, as compared to women. It happens when the hair at the top of the cleft (of the buttocks) gets pushed inside the body, causing dirt to push inside. The condition gets very painful at this stage. In a lot of cases, pilonidal sinus develops from an abscess.