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sebaceous cyst, epidermoid cyst
Cysts are "Sebaceous cyst" is actually a misnomer, since these cysts do not arise from sebaceous glands. The correct name is epidermoid cyst. You will also see "epidermal inclusion cyst" commonly used, but epidermoid cyst is the more general and preferred term.
They are produced when epidermal cells (from the outermost layer of the skin) become implanted within the deeper layer of the skin, the dermis. Subsequent shedding of dead epidermal skin cells into a closed space within the dermis leads to an accumulation of cheesy material that may leak to the surface of the skin. They range in size from a couple of millimeters to over an inch in diameter, and are typically firm, round, mobile under the skin, and are usually slow-growing and painless. They can become infected however, which usually leads to removal. Their color ranges from yellow to white.
The most common areas where these occur are the face, trunk, neck, extremities, and scalp, but these cysts can occur anywhere there is skin. Removal is indicated for cosmetic reasons, or if a cyst becomes infected.