Epidermoid cysts: what they are, causes, symptoms and treatment

The PCDS describes an epidermoid cyst as a very common cyst containing keratin and its breakdown products, surrounded by a wall made of epidermis, the top layer of skin. It sits in the dermis and raises the skin to produce a firm, elastic, dome-shaped lump that moves over the tissues underneath. It may be tethered to the skin, and a central keratin-filled opening (punctum) may be present.

The NHS describes skin cysts in general as round lumps just underneath the skin that often contain fluid or pus, sometimes have a small dark spot in the middle, grow slowly and vary from smaller than a pea to several centimetres across. It lists the epidermoid cyst as a cyst that develops in the top layer of skin.

The PCDS says "sebaceous cyst" is a misnomer for an epidermoid cyst. The NHS says epidermoid cysts and pilar cysts are both sometimes called sebaceous cysts. It describes a pilar cyst as one that forms in a hair follicle, usually on the scalp.

In practice the name matters less than the lump itself: a doctor can usually tell from the appearance and feel what type of cyst it is, and treatment is similar.

The PCDS says epidermoid cysts tend to be symptom-free unless they become infected. They commonly occur on the face, neck, shoulders and chest, and are often multiple. Cysts found near the skin surface are yellow-white, and lesions enlarge slowly. The NHS says skin cysts can form on most areas of the body, including the head, face, neck, chest and back, and on the scrotum or inside the vagina.

• A firm, round, dome-shaped lump under the skin that moves over the tissue beneath.

• A tiny dark or pale central dot (punctum).

• Slow growth over months or years.

• Skin over the cyst that may look yellow-white.

• If infected: the cyst enlarges, becomes red and tender and eventually discharges pus. The NHS notes redness may be harder to see on black or brown skin.

The PCDS says many result from inflammation around a pilosebaceous follicle (hair follicle and oil gland) and can therefore follow on from more severe acne. Some may result from deep implantation of the epidermis by a blunt penetrating injury, called implantation epidermoid cysts, which usually occur on the palms or soles, buttock or knee.

The NHS says anyone can get a skin cyst and it is not always known what causes them. You may be more likely to get one if a family member also has cysts, you are an adult (particularly middle-aged), you are a woman, you have acne, or you have a rare condition such as familial adenomatous polyposis. The PCDS says young and middle-aged adults are most frequently affected, and cysts are rare in childhood.

The NHS says to see a GP if you have a lump on your skin and you do not know what it is. It says to ask for an urgent GP appointment or get help from 111 if you have a sore or red lump on your skin.

The PCDS warns about cysts that have been present from birth or arose in the first few years of life, as they could be dermoid cysts. These form along lines of fusion, most commonly on the head and neck, and can have deep connections, so removal should be by an appropriate specialist.

The PCDS also describes Gardner's syndrome, a rare inherited condition associated with multiple epidermoid cysts (usually on the face, scalp and limbs) together with polyps of the colon, bony growths of the skull and fibromas. Many cysts, particularly at a young age or with a family history of bowel problems, are worth mentioning to a GP.

The NHS says skin cysts do not need treatment if they are not causing problems. Treatment may be recommended for an infected cyst, which may be treated with antibiotics, or for a large painful cyst that interferes with everyday life, such as one on the scalp that catches when you brush your hair.

The NHS is clear that you should not squeeze a skin cyst, and does not recommend home removal. Removal is done by cutting the cyst out under local anaesthetic, leaving a small scar. The NHS notes you may also get new skin cysts in the future.

The PCDS says epidermoid cysts can be dissected out, which is more easily done for cysts that have not been infected. Any recent infection must be allowed to settle for at least six weeks before removal, otherwise the wound is more likely to break down and scar. A cyst that has often been infected may be difficult to dissect out and may be better managed by excision.

The NHS says that if a cyst is large and painful and makes everyday tasks difficult you may be able to have it removed on the NHS. If it causes no problems but is on a visible part of the body, such as the face, you may choose to have it removed, but you will probably have to pay for this privately.

Whether a particular area funds removal varies, so ask your GP what is available locally. Whichever route you use, a cyst that has been surgically removed should normally be checked by the surgeon or GP if the wound becomes red, sore or discharges.