DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Sebaceous cyst on the scalp. Also called a steatoma or wen, this is a cyst arising in one of the skin's oil-secreting glands. Such cysts may grow to a large size; their contents, a yellow, cheese-like sebum, may become infected. They are treated by surgical removal.
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