Sebaceous Cyst

A sebaceous cyst ( /sɪˈbeɪʃəs sɪst/) is a term that loosely refers to either epidermoid cysts (also known as epidermal cysts; L72.0) or pilar cysts (also known as trichilemmal cysts; L72.1). Because an epidermoid cyst originates in the epidermis and a pilar cyst originates from hair follicles, by definition, neither type of cyst is strictly a sebaceous cyst. The name is regarded as a misnomer as the fatty, white, semi-solid material in both of these cyst entities is not sebum, but keratin. Furthermore, under the microscope neither entity contains sebaceous glands. In practice, however, the terms are often used interchangeably.

"True" sebaceous cysts are relatively rare and are known as steatocystomas or, if multiple, as steatocystoma multiplex.