Keratin cyst

Alternative names
Epidermal cyst; Sebaceous cyst; Epidermoid cyst

A sebaceous cyst is a closed sac found just under the skin containing “pasty” or “cheesy” looking skin secretions.

Causes, incidence, and risk factors

Sebaceous cysts most often arise from swollen hair follicles. Skin trauma can also induce a cyst to form. A sac of cells is created into which a protein called keratin is secreted.

These cysts are usually found on the face, neck, and trunk. They are usually slow- growing, painless, freely movable lumps beneath the skin. Occasionally, however, a cyst will become inflamed and tender.


  • usually a nontender, small lump beneath the skin  
  • redness, tenderness, or increased temperature of the skin over the area may occur infection  
  • grayish white, cheesy, foul smelling material may drain from the cyst

Signs and tests

In most cases, your physician can diagnose a cyst based on its appearance. Occasionally, a biopsy may be needed to rule out other conditions with a similar appearance.


Sebaceous cysts are not dangerous and can usually be ignored. At times, they may become inflamed and tender. Others may grow large and interfere with day-to-day life. In these cases, you can have them surgically removed in a physician’s office. Alternatively, small inflamed cysts can be treated by injection of steroid medications.

Expectations (prognosis)
Most cysts may be ignored or treated with simple surgery.

These cysts may occasionally become infected and form into painful abscesses. Recurrence after excision is also not unusual.

Calling your health care provider
Call your health care provider if you notice any new growths on your body. Though cysts are not dangerous, your doctor should examine you to ensure that skin cancer is not present.

Johns Hopkins patient information

Last revised: December 5, 2012
by David A. Scott, M.D.

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All ArmMed Media material is provided for information only and is neither advice nor a substitute for proper medical care. Consult a qualified healthcare professional who understands your particular history for individual concerns.