A sebaceous cyst
is a term that loosely refers to either epidermal cysts or pilar cysts also known as trichilemmal cysts.  The name is regarded as a misnomer as the fatty, white, semi-solid material in both of these cysts entities is not sebum but keratin. Casually, however, the terms are often used interchangeably.

The scalp, ears, back, face and arms are common sites for cysts, though they may occur anywhere on the body except the palms of the hands and soles of the feet. They are more common in hairier areas and could result in hair loss on the skin surface immediately above the cyst. They are smooth to the touch, vary in size, and are generally round in shape. They are generally mobile masses that can consist of fluid, a cottage cheese like substance or bloody material.

An infected cyst may require oral antibiotics or other treatment before and/or after excision.  With surgery, a cyst can usually be excised in its entirety.  Previous infection leading to scarring and tethering of the cyst to the surrounding tissue may lead to rupture during excision and removal. A completely removed cyst will not recur, though if the patient has a predisposition to cyst formation, further cysts may develop in the same general area.
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