An epidermoid cyst is a closed sac under the skin, or a skin lump, filled with dead skin cells.
Epidermal cyst; Keratin cyst; Epidermal inclusion cyst; Follicular infundibular cyst
Epidermal cysts are very common. Their cause is unknown. The cysts are formed when the surface skin is folded in on itself. 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, epidermal cysts are called sebaceous cysts. This is not correct because the contents of the two types of cysts are different. Epidermal 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.)
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:
Epidermal 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:
Cysts may become infected and form painful abscesses.
Cysts may return if they are not completely removed by surgery.
Call your provider if you notice any new growths on your body. Although 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 a cyst, call your provider if it becomes red or painful.
Habif TP. Benign skin tumors. In: Habif TP, ed. Clinical Dermatology: A Color Guide to Diagnosis and Therapy. 6th ed. Philadelphia, PA: Elsevier; 2016: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. 13th ed. Philadelphia, PA: Elsevier; 2020:chap 29.
Patterson JW. Cysts, sinuses, and pits. In: Patterson JW, ed. Weedon's Skin Pathology. 4th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2016:chap 16.
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