An epidermoid cyst is a lump under the skin. Epidermoid cysts usually do not require treatment, unless a person wants to have them removed due to cosmetic reasons, or if the cyst becomes infected.

Epidermoid cysts are usually harmless, but they can have some risks if they rupture or “pop”. It is for this reason that people should not attempt to pop or remove them at home. Only a doctor can do this safely.

In this article, we look at what an epidermoid cyst is, its symptoms, causes, and treatment options. We also discuss when a person should seek medical help.

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An epidermoid cyst is a slow-growing lump that appears under the skin. These cysts are not cancerous, but they can be painful.

A cyst typically has two features: the lining and the contents. The lining of an epidermoid cyst is made up of skin cells, which secrete keratin. Keratin is the material that makes up the hair and the outer layer of skin.

The contents of an epidermoid cyst are soft and “cheese-like”, with an unpleasant smell.

How is it different from a sebaceous cyst?

Some people refer to epidermoid cysts as a sebaceous cysts, but they are not the same thing. Sebaceous cysts are less common, and the contents consist of a clear, oily liquid that the sebaceous glands produce.

The main symptom of an epidermoid cyst is a lump, which can become painful if there is inflammation or an infection. A person is typically able to move the cyst slightly under the skin.

Epidermoid cysts vary in size from a tiny bumps to growths larger than a golf ball. Tiny epidermoid cysts are known as milia, or milk spots.

There may be a small dark pore-like “punctum” that indicates the opening of the cyst. Inside the cyst may be a yellowish, unpleasant-smelling material similar to soft cheese.

Epidermoid cysts can appear anywhere on the body but typically appear on the:

  • face
  • ears
  • neck
  • chest
  • upper back
  • scrotum
  • vulva

Approximately 7% of epidermoid cysts develop in the head or neck area.

Epidermoid cysts usually occur when there is a blockage of the hair follicle, which causes a cyst to form. As a result, they are common in people who experience acne, as they tend to have more blocked pores.

An epidermoid cyst may also form at the site of injury to the body.

An epidermoid cyst may not need treatment as long as it is fairly small and not in an awkward place on the body. However, a healthcare professional may recommend removal if:

  • there are signs of infection
  • the cyst is large or prevents certain movements
  • the cyst interferes with everyday life

Some people may also elect to have treatment for a cyst for cosmetic reasons.

When treatment is necessary, a medical professional may remove the cyst through surgical excision. This is the most effective treatment, as it reduces the risk the cyst will come back. However, it may not work as effectively if the cyst has ruptured.

For the procedure, a doctor will use a local anesthetic to numb the area, then aim to remove the whole cyst intact. If excision is not possible, they may drain it with a needle instead.

If an infection has occurred, a person may also need antibiotics.

After excision, a person may experience some swelling or pain while the wound heals. The procedure also has some risks. It may result in:

  • damage to the surrounding tissues
  • bleeding
  • scarring
  • infection

According to DermNet, epidermoid cysts most commonly occur in adults. They are twice as common in males than in females, but the reasons for this are unclear.

A person may also be more likely to develop epidermoid cysts if they have certain genetic disorders, including:

The most common complications of epidermoid cysts occur if the cyst ruptures. It can result in:

  • swelling
  • pain
  • inflamed skin
  • localized cellulitis, which is a deep skin infection

It is for this reason that people should not try to pop or otherwise treat cysts themselves at home. Doing this can cause further damage.

A 2018 literature review notes that rarely, epidermoid cysts can become malignant, or cancerous. Cutaneous squamous cell carcinoma, basal cell carcinoma, and Merkel cell carcinoma can begin in an epidermoid cyst.

At the first consultation, a doctor may physically examine the lump, looking for clinical signs that it is movable, and has a central dot, or punctum. This can indicate it is a cyst, and not something else.

If it is unclear what the lump is, they may ask further questions or recommend testing, such as an ultrasound scan. However, this is usually not necessary for epidermoid cysts.

After an excision, medical professionals may analyze the contents in a laboratory to confirm that the lump is only a cyst, and not something more serious.

Anyone who has a lump under the skin with an unknown cause should speak with a doctor, particularly if it occurs with other symptoms, such as pain and inflammation. A doctor can identify what it is and whether it requires treatment.

Speak with a doctor promptly if the cyst:

  • pops or ruptures
  • becomes swollen and inflamed
  • oozes pus
  • is in an unusual or awkward place, such as the fingers or genitals
  • is at risk of rupturing due to its location

Contact a doctor as soon as possible if a lump begins growing or changing quickly, even if a doctor previously diagnosed it as an epidermoid cyst.

The outlook for epidermoid cysts is usually positive. Most epidermoid cysts are harmless, and excision can prevent them from returning, as long as a doctor removes the entire sac.

However, if the cyst has ruptured, it can be difficult to remove it completely. This can increase the chance of recurrence.

Rupturing can also pose a risk of infections, inflammation, and damage to the surrounding tissue.

Epidermoid cysts are harmless growths that occur due to a blocked hair follicle. They contain a soft, cheese-like substance known as keratin.

These cysts do not typically need treatment. However, they can sometimes cause distress, and may become inflamed or infected.

A person should see a healthcare professional to receive a correct diagnosis, as many conditions can cause lumps. A doctor can identify the condition and advise on the next steps.