Trichilemmal Cyst

A trichilemmal cyst, also known as a wen, pilar cyst or isthmus-catagen cyst, is a common cyst that forms from a hair follicle. They are most often found on the scalp. The cysts are smooth, mobile and filled with keratin, a protein component found in hair, nails, and skin. They may or may not be tender. Trichilemmal cysts may run in families. Rarely, these cysts may grow more extensively and form rapidly multiplying trichilemmal tumors, also called proliferating trichilemmal cysts, which are benign but may grow aggressively at the cyst site. Very rarely, trichilemmal cysts can become cancerous.