Patient with a sebaceous cyst on their foot. Sebaceous cysts are common noncancerous cysts of the skin. Cysts are abnormalities in the body that may contain liquid or semi-liquid material. Sebaceous cysts are mostly found on the face, neck, or torso. They grow slowly and are not life threatening, but they may become uncomfortable if they go unchecked. Doctors usually diagnose a cyst with only a physical examination and medical history. In some cases, a cyst will be examined more thoroughly for signs of cancer.