“Normal” human skin cells can contain a surprisingly large number of sun-induced mutations in their DNA, a new study has found. Philip Jones, a cancer researcher at the Wellcome Trust Sanger Institute in the U.K., and colleagues took samples of cells from eyelid skin discarded during plastic surgery procedures. By sequencing the DNA in those skin samples, they were able to develop a picture of the types of mutations that can accumulate in skin cells over time. They found that over a quarter of normal, sun-exposed skin cells carry at least one “driver mutation” that can give that cell a reproductive advantage. The scientists are working to understand the factors that lead some cells to become cancerous.