SEBACEOUS CYST

A sebaceous cyst is a term commonly used to refer to either

Epidermoid cysts (also termed epidermal cysts, infundibular cyst)

Pilar cysts (also termed trichelemmal cysts, isthmus-catagen cysts)

Both of the above types of cysts contain keratin, not sebum, and neither originates from sebaceous glands. Epidermoid cysts originate in the epidermis and pilar cysts originate from hair follicles. Technically speaking, then, they are not sebaceous cysts.

 "True" sebaceous cysts, which originate from sebaceous glands and which contain sebum, are relatively rare and are known as steatocystoma simplex or, if multiple, as steatocystoma multiplex.

Medical professionals have suggested that the term "sebaceous cyst" be avoided since it can be misleading.In practice, however, the term is still often used for epidermoid and pilar cysts.

About 90% of pilar cysts occur on the scalp, with the remaining sometimes occurring on the face, trunk, and extremities.Pilar cysts are significantly more common in females, and a tendency to develop these cysts is often inherited in an autosomal dominant pattern.In most cases, multiple pilar cysts appear at once.