As much as 25% of the skin of middle-aged people may contain cancer-linked mutations, researchers said last night.
The findings show the effect of age on the skin – not necessarily increasing risk of cancer.
They come from a scientific study aimed at tracking the development of skin cancer.
Researchers studied samples from four patients aged between 55 and 73 after they underwent surgery to remove excess skin on the eyelids.
Researchers said "almost certainly" none of the mutated cells would have developed into skin cancer.
The researcher was conducted at the Wellcome Trust Sanger Institute, Cambridge, UK, and reported in Science.
Researchers found more than 100 cancer-linked mutations per square centimetre of skin. From 234 biopsies, the researchers found 3,760 mutations.
Researcher Dr Iñigo Martincorena said: “The burden of mutations observed is high but almost certainly none of these clones would have developed into skin cancer.
“Because skin cancers are so common in the population, it makes sense that individuals would carry a large number of mutations. What we are seeing here are the hidden depths of the iceberg, not just the relatively small number that break through the surface waters to become cancer.”
Fellow researcher Dr Phil Jones added: “These kinds of mutations accumulate over time – whenever our skin is exposed to sunlight, we are at risk of adding to them.
“Throughout our lives we need to protect our skin by using sun-block lotions, staying away from midday sun and covering exposed skin wherever possible. These precautions are important at any stage of life but particularly in children, who are busy growing new skin, and older people, who have already built up an array of mutations.”
Martincorena I, et al. High burden and pervasive positive selection of somatic mutations in normal human skin. Science 21 May 2015 [abstract]
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