An epidermoid cyst is a small 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.

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.

A epidermoid cyst on the back of a person's neck.Share on Pinterest
Photography courtesy of Steven Fruitsmaak/Wikimedia

An epidermoid cyst is a slow-growing, painless lump. According to the British Association of Dermatology, epidermoid cysts are common and not cancerous.

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?

People may have previously referred to an epidermoid cyst as a sebaceous cyst.

This is incorrect. Sebaceous cysts are less common, and the contents consist of a clear, oily liquid that the sebaceous glands produce.

Epidermoid cysts are usually painless unless they become inflamed or infected. A person is typically able to move the cyst slightly.

Epidermoid cysts vary in size from a small lump to bumps larger than a golf ball. Tiny epidermoid cysts are known as milia, and can occur in infants.

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

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 allows 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 trauma to the body.

Epidermoid cysts can be left alone, as long as they are not located in an awkward place on the body, and are small. However, a healthcare professional may recommend removal:

  • if they are infected
  • if they interfere with everyday life
  • for cosmetic reasons

In these cases, a medical professional will remove the cyst through surgical excision in an office procedure. They will use local anesthetic and will aim to remove the cyst intact to minimize the risk of it recurring.

If an infection has occurred, a person may need antibiotics, and a healthcare professional may drain the cyst.

According to DermNet, epidermoid cysts most commonly occur in adults, and are twice as common in males than in females.

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

  • basal cell nevus syndrome
  • pachyonychia congenita type 2
  • Gardner syndrome

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

After excision, a person may experience:

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

Sometimes, medical professionals may recommend an ultrasound to check if the lump on a person’s body is an epidermoid cyst.

A 2018 literature review notes that epidermoid cysts can rarely become malignant. Cutaneous squamous cell carcinoma, basal cell carcinoma, and Merkel cell carcinoma can arise within an epidermoid cyst.

Conditions that a doctor may rule out before diagnosing a person with an epidermoid cyst include:

  • lipoma
  • pilar cyst
  • abscess
  • dermoid cyst
  • steatocystoma
  • carcinoma

It may be the case that a doctor does not fully diagnose an epidermoid cyst until after its removal. At the time of excision, they may check the removed material under a microscope to be sure that it was simply an epidermoid cyst, as opposed to anything to be concerned about.

Epidermoid cysts are harmless, but people should seek medical attention if they appear to be growing in size quickly. They can also seek medical advice if the cyst is in a location that affects the ability to perform daily activities.

Some people may be able to ignore their epidermoid cyst and live with it, while others may want it removed for cosmetic reasons. This is when they should see a doctor.

A person should also see a doctor if they notice that the cyst:

  • ruptures
  • becomes inflamed
  • is in a location that is easily irritated or knocked frequently
  • occurs in an unusual place, such as fingers or genitalia

It is important not to try to remove an epidermoid cyst at home. Trying to remove it at home can result in scarring or other complications.

Providing that a dermatologist removes the entire sac wall, the cyst should not return.

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

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

They do not typically need treatment. However, a person should seek medical attention if the cyst is causing them cosmetic distress, or if the cyst becomes inflamed or infected.

A person should see a healthcare professional to receive a correct diagnosis.