A typical sebaceous cyst, also called an epidermoid cyst, contains keratin and sebum because it arises from the infundibulum of a hair follicle where keratinocytes proliferate abnormally. These cysts are lined by stratified squamous epithelium that desquamates keratin into the cyst cavity, mixing with oily sebum produced by sebaceous glands. This composition explains the characteristic cheesy, foul-smelling material expelled upon rupture or incision. For surgical excision, complete removal of the cyst wall is essential to prevent recurrence, as leaving the lining behind leads to refilling with keratinous debris. Understanding the contents aids in differentiating these cysts from infectious abscesses that contain pus.

Reference: Robbins Basic Pathology, Kumar V, Abbas A, Aster J, 10th Edition.