Humans could live for hundreds of years as scientists develop treatments to "cure" old age like any other disease, a US researcher said Thursday.Michigan State University clinical professor of medicine Michael Fossel said researchers had already "rejuvenated" skin cells in the laboratory and the potential existed to expand the technolgy to turn back the entire ageing process. "We're altering the amount of gene expression and in skin cell tissue in the labratory we can actually reset the clock and take old cells and make them act like young cells," he told AFP. "The question that we want to ask ourselves is 'can we do this to people?' "The idea that you cannot reverse ageing in cells or tissue is wrong, you can. We just don't know if it will be useful clinically, a lot of us suspect it will but we haven't tested it yet." Fossel, in Sydney to address a conference on longevity, said scientists had altered the way cells act. "What we essentially do is reset the cells to do what they used to do when you were young," he said. "We don't change them, alter them, no we just reset them to do exactly what they did decades prior to what they're doing now. "What sets the clock in you is a change in gene expression that occurs as you get older. It has to do with dividing cells and the damage they cause to all the other cells. "For example, in your heart, when people die of heart attacks they die because their vessels have problems, and that clock is set right in the cells that lie in the vessels and what we can do is reset those clocks. So the question is what happens when we do it? In the lab it works beautifully, but again it's different trying it in people."