Originally published by Harvard Health.
What Is It?
An epidermoid, or epidermal, cyst is a small, movable lump under the skin. It forms when surface skin cells move deeper into the skin and multiply. These cells form the wall of the cyst and secrete a soft, yellowish substance called keratin, which fills the cyst. If the wall of the cyst is ruptured, the keratin is discharged into the surrounding skin, which causes irritation and inflammation.
The cyst may remain small for years, or it may continue to get larger. These cysts are rare in children but common in adults. Cysts are not cancerous.
A cyst is a movable, dome-shaped, smooth-surfaced mass that varies in size from a few millimeters to several centimeters (from less than a quarter of an inch to more than 2 inches). Epidermoid cysts can occur on almost any skin surface.
Your doctor can examine the swelling and tell you if you have a cyst.
A cyst may disappear on its own or remain indefinitely.
There is no way to prevent epidermoid cysts.
An epidermoid cyst usually does not need to be treated unless it is inflamed (red and tender) or is causing a cosmetic problem. Inflamed cysts usually are treated by draining the fluid and removing the shell that makes up the cyst wall. You also may be treated with antibiotics if the skin around the cyst is also inflamed. If a cyst is causing irritation or cosmetic difficulty, your physician can remove it by making a small incision in the skin and emptying the contents of the cyst and its wall.
When To Call a Professional
If you have a new swelling on your skin that lasts for more than two weeks, contact your doctor, especially if it is painful.
The outlook for epidermoid cysts is excellent. Many cysts have no symptoms and some will go away on their own. Cysts can return. If your cyst is problematic, your doctor may decide to drain it or remove it surgically. This does not usually lead to any complications or side effects.
American Academy of Dermatology
P.O. Box 4014
Schaumburg, IL 60168-4014