Which of the following describes a Cock's peculiar tumour?

Cocks peculiar tumour is a complication of sebaceous cyst. It occurs when the surface of the sebaceous cyst gets ulcerated leading to the formation of a painful, fungating mass with discharge. It often resembles epithelioma. Sebaceous cyst is a retention cyst which result from a blockage of the duct of the sebaceous gland causing a cystic swelling. It has a putty like consistency with a parasite in the wall of the sebaceous cyst called demodex folliculorum. Other complications of a sebaceous cyst are: Infection and abscess Sebaceous horn formation which result from hardening of a slowly discharged sebum through the punctum. Ref: Srb's Manual of Surgery by Bhat By Jaypee Brothers, page 22.