A discovery by Cambridge scientists about the way our skin cells are constantly renewed could shed light on the development of dangerous cancers.
The researchers watched skin cells growing over a year.
The team from the MRC Cancer Cell Unit was surprised to see mouse skin cells dividing in a different way to many other cells in the body.
The find, detailed in Nature, could help reveal why some cells can become cancerous and cause tumours.
However, it does not yet translate into new cancer treatments, experts say.
Everyday we shed the outermost layer of our skin, replacing it from within with a new supply of skin cells.
Until now, the conventional view of this 'conveyor belt' of new skin cells involved two key types of cell working in tandem.
Stem cells in the base layer of the skin were thought to produce short-lived cells that soon stopped dividing by themselves.
However, no-one had actually documented this process in action, and the Cambridge researchers, using mice, were able to pick out specific genes with a fluorescent marker in order to plot these changes under the microscope.
The cells were followed closely as they divided within the skin over a period of a year.
They found their expectations reversed, with stem cells playing very little part in proceedings in normal skin, only swinging into action if the skin was unhealthy or damaged, in order to carry out repairs.
Cells 'gone bad'
Instead, the cells previously thought to be short lived carried on dividing, but instead of producing two flourishing cells after each division, one of the cells stops growing, leaving one remaining cell to carry on the process.
Dr Philip Jones, who led the research, said that the finding might help scientists understand what is going wrong when a skin cancer begins to develop.
"One of the implications of what we've seen is that these progenitor skin cells can potentially go bad and cause skin cancer if they linger long enough."
Tracking these cells in animals at a cellular level over a whole year allowed the scientists to come up with mathematical models to predict what happens to our skin over long periods.
This may eventually increase knowledge of the role of different genes in the maintenance of healthy skin - and in the growth of cancers.
Dr Jones said: "Our ultimate goal though is to be able to model the evolution of cancer from the single cell stage onwards so we can find better ways to tackling the disease. By using the right gene to label the cells, this might just be possible."
Professor Ian MacKenzie, a researcher in stem cell biology from the Queen Mary School of Medicine and Dentistry in London, said that it was still likely that stem cells played a significant role in the development of cancer.
"If this is true, and you have another type of cells hanging around for a long time, then it changes the idea that cancer arises from stem cells - but I'm not entirely convinced by this.
"By the time the cancer arises it has certainly got a stem cell component, and while it's very interesting, I'm not sure that it will have an impact on the way cancer is treated."