DR P. MARAZZI / SCIENCE PHOTO LIBRARY DR P. MARAZZI / SCIENCE PHOTO LIBRARY
Cryotherapy blister on the skin of a 40-year-old woman. The blister is the result of using liquid nitrogen to freeze off a benign raised naevus (or mole). Nitrogen liquifies at -198 degrees Celsius, and this freezing kills the tissue in and around the skin lesion. This blister forms as part of the healing process, eventually becoming a scab that drops off, sometimes leaving a faint scar.
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