What Is an Epidermoid Cyst?

Epidermoid cysts are non-cancerous, balloon-like bumps that slowly develop under the skin. They are filled with a substance called keratin and can range in size from less than 1/4 inch to several inches wide. The cysts can sometimes rupture and drain a thick, yellow, foul-smelling fluid.

Epidermoid cysts can appear anywhere but are most often seen on the face, scalp, trunk, groin, and upper back. Though typically harmless, the cysts may require treatment if they become enlarged or infected.

This article describes the symptoms and causes of epidermoid cysts as well as how they are diagnosed, treated, and prevented.

What Are the Symptoms of Epidermoid Cysts?

An epidermoid cyst looks like a raised, round bump. Like all cysts, it is filled with fluid.

With an epidermoid cyst, you can usually feel the cyst wall and move the cyst around fairly easily under the skin. There may also be a small, pore-like opening on the surface of the skin.

Other symptoms of an epidermoid cyst include:

• Pain and pressure under the skin
• Tenderness when touched
• Redness and swelling
• A yellowish, thick discharge with a foul odor
  

When to See a Healthcare Provider

Epidermoid cysts usually don't cause any problems, but you should see a healthcare provider if it is:

• Fast-growing
• Very large
• Painful, red, and hot
• Leaking fluid
  

If the cyst wall ruptures, it can lead to an infection.

What Causes Epidermoid Cysts?

Epidermoid cysts are the most common type of skin cyst. They occur when epidermal cells—those that make up the outermost layer of skin called the epidermis—don't shed properly and move beneath the skin's surface.

Epidermal cells produce a type of protein called keratin that makes up your skin, hair, and nails. When these cells are trapped beneath the skin, they will continue to produce keratin, leading to the formation of a fully contained, fluid-filled cyst.

The entrapment of epidermal cells may be caused by an injury, surgery, or body piercing. Some occur spontaneously for no known reason. On rare occasions, they can occur with genetic disorders like pachyonychia congenita.

How Are Epidermoid Cysts Diagnosed?

Epidermoid cysts account for the majority of cysts seen by dermatologists, and they can often be diagnosed by their appearance alone.

If needed, an ultrasound (which produces images using sound waves) can help visualize the structure, position, and size of the cyst. The cyst wall will be clearly seen on an ultrasound, while the center of the cyst will look like ground glass.

To confirm the diagnosis, the dermatologist may want to rule out other possible causes (differential diagnosis), including:

• Nodular acne: A severe type of acne that causes hard lumps or knots
• Sebaceous cyst: A type of cyst caused by a plugged sebaceous gland
• Furuncle: Also known as a boil
• Lipoma: A harmless fatty tumor located just below the skin
• Sebaceous hyperplasia: Skin-colored bumps caused by overactive sebaceous glands

An in-office biopsy can be performed to obtain a tissue sample for a pathologist to examine under a microscope. When seen up close, the cells will look clumped, fibrous, and horn-like.

How Are Epidermoid Cysts Treated?

An epidermoid cyst doesn't usually have to be treated if small and painless. Even so, some people may want it drained for cosmetic reasons, especially if it is on the face.

The draining of a cyst should be done by a healthcare provider under sterile conditions. Afterward, you may be advised to use a warm compress for a few days to help the cyst drain. The warmth can also help promote healing by increasing blood flow to the injury.

If the cyst is especially large or inflamed, a corticosteroid (steroid) injection can help reduce swelling and redness. Kenalog (triamcinolone) is commonly used for this.

Oral antibiotics may be prescribed if the cyst is infected (or to prevent infection following the cyst drainage).

Epidermoid Cyst Removal

Your healthcare provider may recommend the removal of an epidermal cyst if it is severe, recurs (comes back), or is located in a place where is continually irritated (such as around the collar or where your glasses touch the skin of your ear). You may also request that a cyst be removed for cosmetic reasons.

To remove the cyst, your healthcare provider will first make an incision to extract the keratin content. The cyst wall will then be separated from the surrounding tissues and removed with a pair of forceps or tweezers. If the incision is large, stitches or surgical glue may be needed.

By removing the cyst in its entirety, the trapped epidermal cells will no longer produce keratin and the cyst will no longer recur.

Summary

An epidermoid cyst is a common, harmless cyst filled with keratin. Small cysts usually don't need to be treated. Sometimes a cyst will grow large and need to be drained. Treatment may also involve antibiotics or a corticosteroid injection.

You may want your cyst removed for cosmetic reasons or because it is large and irritating. To remove the cyst, your healthcare provider will first drain it and then remove the cyst wall. Never attempt to remove an epidermoid cyst on your own.