More than a quarter of middle-aged people’s skin cells may have already mutated into cancerous tissue, according to a new study published in the journal Science.

Researchers from the Sanger Institute near Cambridge, UK, analysed samples from a group of 55 to 73-year olds and found more than 100 DNA mutations linked to cancer in every 1sq cm (0.16sq in) of skin. Samples were taken from excess skin removed from the eyelids of patients. The researchers then drilled down into the skin’s DNA.

“The most surprising thing is just the scale,” Dr Peter Campbell, head of cancer genetics at Sanger, told the BBC. “That a quarter to a third of cells had these cancerous mutations is way higher than we’d expect, but these cells are functioning normally.”

It would take multiple mutations, however, to culminate in a tumour and no one is sure exactly how many.

“It drives home the message that these mutations accumulate throughout life and the best prevention is a lifetime of attention to the damage from sun exposure,” added Campbell.

Stating that prevention is the first line of defence, sunscreen lotions and protective clothing were highlighted by Campbell as the best protection.

Recently, a consumer watchdog found certain well-known suncare brands did not meet sun protection safety requirements, highlighting the need for rigorous testing to ensure standards.