Cysts

What are skin cysts?

Skin cysts are common, harmless lumps under the skin. The two most common types are epidermoid cysts and pilar cysts. Both are small sacs lined by skin cells and filled with keratin, a soft, cheesy protein that the skin normally produces. They are sometimes incorrectly called sebaceous cysts.

The commonest kind is the epidermoid cyst. Typical sites are the face and neck, behind the ears, the chest and upper back, and the genital area. They often have a small dark opening on the surface called a punctum. They can form without any clear cause, or after skin damage or irritation pushes surface skin cells deeper, where they multiply. Pilar cysts, also called trichilemmal cysts, develop from the root sheath of hair follicles. They occur most commonly on the scalp. They are smooth, firm and mobile, usually have no central opening, and often occur in multiples. They are more common in middle-aged women and run strongly in families.

Who gets them?

Skin cysts are common. Epidermoid cysts usually affect young and middle-aged adults and are about twice as common in men, while pilar cysts are more common in middle-aged women. Multiple cysts, particularly at a young age, can occasionally be associated with rare inherited conditions.

What causes them?

Cysts form when skin cells that would normally be shed from the surface end up beneath it and continue to produce keratin, which collects inside a sac. Epidermoid cysts can form without any clear cause, or after skin damage or irritation. Pilar cysts develop from the lining of the hair root.

Are they hereditary or contagious?

Pilar cysts frequently run in families, and each child of an affected parent can have a 50 in 100 chance of developing them. Epidermoid cysts are not usually inherited. Cysts are not contagious and are not related to hygiene.

What do they look and feel like?

Cysts are smooth, round, dome-shaped lumps that sit just under the skin and usually move slightly when pressed. Most are skin-toned, white or yellowish, and they can be anything between a few millimetres and several centimetres in size. They grow slowly and are usually painless. Cysts on the scalp can catch on a comb or brush.

If squeezed, an epidermoid cyst can release thick, cheesy, white or yellow material with an unpleasant smell.

Cysts can become inflamed, often if they are squeezed, knocked or rupture under the skin. An inflamed cyst becomes red or darker, swollen, hot and painful, and may discharge pus. This is usually an inflammatory reaction to the keratin rather than a true infection, though infection can occur. Repeated inflammation can cause scarring and make the cyst stick to the surrounding tissue.

How are they diagnosed?

Cysts are usually diagnosed from their appearance and feel. Occasionally, an ultrasound scan is used if the lump is unusual. Any lump that grows rapidly, feels hard or fixed, or behaves unusually should be assessed.

What are the treatment options?

Dr Mounsey will confirm the type of cyst. Cysts that cause no problems can be left alone. Inflamed cysts may settle with antibiotics or a steroid injection, and may need to be drained if very swollen. Cysts that are troublesome or keep becoming inflamed can be removed by excision under local anaesthetic, which he carries out himself. Removing the whole cyst wall reduces the chance of it returning, and this is best done when the cyst is not inflamed.

What is the outlook?

Cysts are harmless and very rarely become cancerous. They do not go away on their own and may slowly enlarge or become inflamed from time to time.

More information

British Association of Dermatologists patient leaflet: https://www.bad.org.uk/pils/cysts-epidermoid-and-pilar

This page gives general information only and is not a substitute for a consultation. Everyone's skin is different, and what is right for you will depend on your own circumstances. If you are worried about a skin problem, please book an appointment with Dr Mounsey or speak to your GP. If you have a mole or skin lesion that is changing, bleeding or growing quickly, please seek medical advice promptly.