Engineers and biologists from the University of Sheffield have found that the theory of "sleeping" stem cells best explains the mechanism behind the regeneration and aging of skin.

The skin is known to be the largest organ of the human body. Though many theories exist on how skin constantly grows and sheds off the old, scientists are yet to agree upon a single explanation for it. A new study by the researchers from the University of Sheffield may have finally found a solution. One of the popular theories says the skin has "sleeping cells" , which can be woken up when the need arises.

Researchers of this new study created an "in silico" (computer), "visual" model of the human skin and then used it to test the three most popular theories of how skin cells function to regenerate our skin for a period of three years.  When the model stimulation was tested with two theories, the skin failed to regenerate. However, with the third theory, the skin showed signs of regeneration.

"The theory which seems to fit best says that skin has a population of 'sleeping' stem cells, which sit in the lowest layer of the skin but don't constantly divide to make new cells," Dr. Xinshan Li (University of Sheffield Faculty of Engineering) said in a news statement. "However, these sleeping cells can be called into action if the skin is damaged, or if the numbers of other types of more mature skin cells decrease, ensuring that the skin can be constantly regenerated under all conditions."

Li goes on to explain the functioning of this theory. He notes that these sleeping cells are gradually lost over time, which results in the aging of skin. Each time these cells are woken to either heal a wound or grow new skin, a few of them don't go back to sleep. Thus, with time, their quantity in the body is reduced. This also provides an explanation as to why older skin takes longer to heal.

Computer modeling of skin biology has proved to be very useful for scientists as it allows them to study organs like skin that are difficult to follow in live systems for extended periods. Current models are viable for only a few weeks and clinical studies in humans are only practical for a few months.

This new study was conducted in collaboration with The Procter & Gamble Company (P&G), makers of Olay and its findings can be used to for ways to combat the effects of aging on our skin, authors of the study suggest.