DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Sebaceous cyst. Close-up of a sebaceous cyst on a 39-year-old male patient's back. A sebaceous cyst is a sac-like swelling under the skin filled with sebum, the oily product of the skin's sebaceous glands. It occurs when the glands becomes blocked. Most cysts heal on their own, but some require surgical removal.
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