What are epidermoid and pilar cysts?
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).
- An epidermoid cyst is a cyst where the cyst sac forms from cells that normally occur on the top layer of the skin (the epidermis).
- A pilar cyst is a cyst where the cyst sac forms from cells similar to those that are in the bottom of hair follicles (where hairs grow from).
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.
What do these cysts look like and what are their symptoms?
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. The picture shows a cyst in the neck that could be either an epidermoid or a pilar cyst.
- Epidermoid cysts can affect anyone but are most common in young and middle-aged adults. They can appear anywhere on the skin but develop most commonly on the face, neck, chest, and upper back.
- Pilar cysts can affect anyone but are most common in middle-aged women. They can appear anywhere on the skin but develop most commonly on the scalp. It is common for several to develop at the same time on the scalp.
Both epidermoid and pilar cysts usually cause no symptoms. Occasionally:
- They become infected, when they may become red, inflamed and painful. A course of antibiotics will usually clear an infection if it occurs.
- The cyst may leak the ‘toothpaste-like’ material on to the skin if the cyst is punctured or damaged.
- A little ‘horn’ may grow on the skin over the cyst.
- A cyst may form in an uncomfortable place such as in the genital skin or beside a nail.
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 many 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.