Epidermoid and pilar cysts look like small smooth lumps under the skin surface. They are benign (non-cancerous) and usually cause no harm or problems. If required, they can usually be removed easily by a small operation done under local anaesthetic. The main reason why some people want them removed is for cosmetic reasons, as they can look unsightly.
A cyst is a sac that is filled with a fluid or semi-fluid material. Cysts develop in various places in the body and arise from different tissues in the body. Two of the most common types of cyst that occur under the skin surface are epidermoid and pilar cysts. These cysts used to be called sebaceous cysts but this term is no longer correct, as the origin of these cysts is not from the sebaceous glands in the skin (as was once thought).
In both cases, the semi-fluid content of the cyst looks a bit like toothpaste. This substance is soggy keratin. Keratin is made by skin cells and is the substance that hairs are made from and the substance that covers the top layer of the skin.
Both epidermoid and pilar cysts are smooth round lumps which you can see and feel just beneath the skin surface. They are very common. Often they are small (pea size) but sometimes they slowly get bigger over many months to become a few centimeters in diameter. They look very similar to each other but can be distinguished from each other if the cells that form the cyst sac are looked at under the microscope.
Both epidermoid and pilar cysts usually cause no symptoms. Occasionally:
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 many epidermoid cysts as one of their features.
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.
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.
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.