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What are epidermoid and pilar cysts?

A cyst is a closed sac (think of a pea within a shell) that has two main features:

  • A lining or cyst wall
  • Contents that are liquid or semi-solid

Both types of cyst contain a cheesy material that can have a slight odour. They are made up of keratin, one of the proteins that makes up the outer layer of the skin. Pilar and epidermoid cysts are still occasionally known as sebaceous cysts, but this is a historical term that should no longer be used.

Epidermoid and pilar cysts are common, not cancerous and not contagious.

What causes cysts?

Epidermoid cysts affect young and middle-aged adults. They are thought to arise from a blocked hair follicle. They are common in acne, when excess skin blocks a pore, trapping bacteria deeper down, causing an infected cyst. Epidermoid cysts are most common on the face, neck, genital skin and upper trunk. Epidermoid cysts are usually solitary and not usually inherited.

Pilar cysts usually occur in the scalp. They often run in families and patients may develop multiple pilar cysts over time.

Are cysts harmful?

They are harmless, benign growths but can cause problems due to infection and discomfort when they grow in size or become traumatized.

What do these cysts look like?

They are round, dome-shaped bumps, lying just under the skin surface. Some are yellow or whitish. A small dark plug is often present, through which it may be possible to squeeze out some of the cyst’s contents. The cysts range in size from the size of a pea to those that are several centimeters across.


What are their symptoms?

Both types of cyst grow slowly. Epidermoid cysts can become infected (red and sore) from time to time. They may then discharge cheesy foul-smelling pus. Scalp pilar cysts rarely become infected but can catch on the comb or brush.

How will they be diagnosed?

It is usually possible for your doctor to make a diagnosis based on the appearance alone. If there is any doubt, the cyst can be removed surgically and checked under the microscope.

Can they be removed?

Epidermoid and pilar cysts are harmless. They only need removing when they become medically symptomatic with repeated infection or significant discomfort. We would not normally remove a cyst whilst it is infected because there is a high risk of infection in the wound and poor wound healing. A course of antibiotics will often settle an acute infection and it is not uncommon for some cysts to resolve without treatment.

If they do need surgery, it is a relatively straightforward procedure carried out under local anaesthetic. It is important that the doctor removes the whole of the lining during the operation to minimize the chance of the cyst growing back. With any cyst surgery there is always a risk of recurrence and permanent scarring, especially if surgery has to be carried out urgently.

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