By late middle age, about a quarter of skin cells carry cancer-driving mutations caused by exposure to sunlight — and it’s perfectly normal.
Researchers had previously thought that the types of mutations that fuel tumor growth were rare and happened just before a cell becomes cancerous. But a study of the eyelids of four people who don’t have cancer reveals that such mutations “are staggeringly common in normal skin,” says Philip Jones, a clinical scientist at the University of Cambridge.