What causes epidermoid and pilar cysts?

It seems that some cells that are normally near to the surface of the skin (cells of the epidermis or cells in hair follicles) get into deeper parts of the skin but continue to multiply. This may occur for various reasons. For example, following an injury to the skin. The cells that multiply form into a sac and produce the keratin that they would normally make on the top layer of the skin. The keratin becomes soggy and forms into a toothpaste-like substance.
A tendency to form pilar cysts runs in some families. So, there is a genetic factor in some cases. Epidermoid cysts in themselves are not hereditary and most form for no apparent reason in healthy people. However, some people with rare syndromes have epidermoid cysts as one of their features.

Are epidermoid and pilar cysts harmful?

Not usually. If they do not bother you then it is best just to leave them alone. Sometimes a person with an epidermoid or pilar cyst requests that it be removed. This is usually for one of three reasons.

• Cosmetic reasons. For example, the cyst is in an obvious site on the skin and looks unsightly.
• They are sometimes easy to 'catch' and traumatise. This typically occurs on the scalp when combing hair.
• If the cyst has become infected or irritating.

Epidermoid and pilar cysts are benign. That is, they are not cancerous, do not spread to other parts of the body or cause any serious problems. Very rarely, a skin cancer may develop from an epidermoid or pilar cyst.

Removal of epidermoid and pilar cysts

If required, the cyst can usually be easily removed by a simple operation under local anaesthetic. The surrounding skin is 'numbed' by injecting some local anaesthetic. A small incision (cut) is made over the cyst. Typically, the cyst can be easily pulled out. The wound is then stitched up. A small scar will result. Sometimes after the removal of a cyst it gradually regrows in the same site under the scar. This is unusual, but if it occurs it can be removed again. © EMIS 2009    Reviewed: 21 Jul 2009