Kystes épidermoïdes et pilaires

What are 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 are often 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.

Many doctors still call them sebaceous cysts, though.

What is an epidermoid cyst?

An epidermoid cyst is a cyst where the cyst sac forms from epidermal cells that normally occur on the top layer of the skin (the epidermis).

There are lots of other names for epidermoid cysts, such as epidermal cysts, inclusion cysts, and keratin cysts.

What is a pilar cyst?

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).

A pilar cyst is also known as a trichilemmal cyst.

In both cases, the semi-fluid content of the cyst looks a bit like cottage cheese. 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.

Who gets them?

• 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, upper back and sometimes on the scrotum.

• 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.

Epidermoid and pilar cysts symptoms

Epidermoid and pilar cysts are smooth round lumps which you can see and feel just beneath the skin surface. They are very common.

They range in size but often they are small, like a pea. Sometimes, they can grow slowly over many months to become a few centimetres 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.

Epidermoid and pilar cysts usually cause no symptoms. Occasionally:

• Cysts can become infected, when they may become red, inflamed and painful. A course of antibiotics will usually clear an infection if it occurs. Sometimes they settle down even without antibiotics.

• The cyst may leak the cheese-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.

This photo shows the typical appearance of an epidermoid cyst on someone's neck:

Epidermoid cyst on the neck

© Steven Fruitsmaak (Own work) - close-up view, CC BY-SA 3.0, via Wikimedia Commons

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 and continue to multiply. 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 cheese-like substance and a cyst can occur.

Usually epidermoid cysts pop up for no particular reason: there is nothing you can do to prevent them. They are not related to cleanliness, nor will exfoliating stop them occurring.

Pilar cysts on the scalp can be hereditary and run in families, although this is rare.

Rarely, epidermoid cysts can occur due to genetic disorders. A genetic condition might be present if someone has a lot of epidermoid cysts in unusual locations (like on the fingers and toes).

Are epidermoid and pilar cysts painful?

Not usually. If they do not bother you then it is best just to leave them alone. If one has grown recently it's worth asking your doctor to check that it is a harmless cyst. 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 often becomes infected or irritating.

Epidermoid and pilar cysts are non-cancerous (benign). They do not spread to other parts of the body or cause any serious problems.

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 cut is made over the cyst. It can then be gradually teased out by the doctor. 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.

Bear in mind you then exchange a small cyst for a scar: some people would rather have been left with the cyst, once they see the results of the surgery.