Definition

An epidermoid cyst is a closed sac under the skin, or a skin lump, filled with dead skin cells.

Alternative Names

Epidermal cyst; Keratin cyst; Epidermal inclusion cyst; Follicular infundibular cyst

Causes

Epidermoid cysts are very common. Their cause is unknown. The cysts are formed when elements of the surface skin get under the skin surface. The cyst then becomes filled with dead skin because as the skin grows, it can't be shed as it can elsewhere on the body. When a cyst reaches a certain size, it usually stops growing.

People with these cysts may have family members who also have them.

These cysts are more common in adults than in children.

Sometimes, epidermoid cysts are called sebaceous cysts. This is not correct because the contents of the two types of cysts are different. Epidermoid cysts are filled with dead skin cells, while true sebaceous cysts are filled with yellowish oily material. (A true sebaceous cyst is called a steatocystoma.)

Symptoms

The main symptom is usually a small, non-painful lump beneath the skin. The lump is usually found on the face, neck, and trunk. It will often have a tiny hole or pit in the center. It usually grows slowly and is not painful.

If the lump becomes infected or inflamed, other symptoms may include:

• Skin redness
• Tender or sore skin
• Warm skin in the affected area
• Grayish-white, cheesy, foul-smelling material that drains from the cyst

Exams and Tests

In most cases, your health care provider can make a diagnosis by examining your skin. Sometimes, a biopsy may be needed to check for other conditions. If infection is suspected, you may need to have a skin culture.

Treatment

Epidermoid cysts are not dangerous and do not need to be treated unless they cause symptoms or show signs of inflammation (redness or tenderness). If this occurs, your provider may suggest home care by placing a warm moist cloth (compress) over the area to help the cyst drain and heal.

A cyst may need further treatment if it becomes:

• Inflamed and swollen -- the provider may inject the cyst with steroid medicine
• Swollen, tender, or large -- the provider may drain the cyst or do surgery to remove it
• Infected -- you may be prescribed antibiotics to take by mouth

Possible Complications

Epidermoid cysts may become infected and form painful abscesses.

They may return if they are not completely removed by surgery.

When to Contact a Medical Professional

Contact your provider if you notice any new growths in your body. Although epidermoid cysts are not harmful, your provider should examine you for signs of skin cancer. Some skin cancers look like cystic nodules, so have any new lump examined by your provider. If you do have an epidermoid cyst, call your provider if it becomes red or painful.

References

Dinulos JGH. Benign skin tumors. In: Dinulos JGH, ed. Habif's Clinical Dermatology. 7th ed. Philadelphia, PA: Elsevier; 2021:chap 20.

James WD, Elston DM, Treat JR, Rosenbach MA, Neuhaus IM. Epidermal nevi, neoplasms, and cysts. In: James WD, Elston DM, Treat JR, Rosenbach MA, Neuhaus IM, eds. Andrews' Diseases of the Skin: Clinical Dermatology. 13th ed. Philadelphia, PA: Elsevier; 2020:chap 29.

Patterson JW. Cysts, sinuses, and pits. In: Patterson JW, ed. Weedon's Skin Pathology. 5th ed. Philadelphia, PA: Elsevier Limited; 2021:chap 17.